The interpretation timeline
John 4:38 Douay-Rheims

I have sent you to reap that in which you did not labour: others have laboured, and you have entered into their labours.

A.D. 407 – 1871 5 witnesses

Patristic

before A.D. 750
407
A.D.
John Chrysostom Patristic
A.D. 347–407
“(Hom. xxxiv. 2) I sent you to reap that whereon ye bestowed no labour, i. e. I have reserved you for a favourable time, in which the labour is less, the enjoyment greater. The more laborious part of the work was laid on the Prophets, viz. the sowing of the seed: Other men laboured, and ye are entered into their labours. Christ here throws light on the meaning of the old prophecies. He shews that both the Law and the Prophets, if rightly interpreted, led men to Him; and that the Prophets were sent in fact by Himself. Thus the intimate connexion is established between the Old Testament and the New.”
Source

Scholastic

c. 1100 – 1500
1270
A.D.
Thomas Aquinas Catholic
1225–1274
“Having set forth the slowness of the disciples' understanding concerning the figurative speech, here the Lord consequently explains it, and first he sets forth the explanation of the figurative speech; second he employs a comparison, at the place: "Do you not say, There are yet four months, and then comes the harvest?" Concerning the first, it should be known that just as Christ above explained to the woman what he had figuratively proposed to her about water, so also he explains to the apostles what he had figuratively proposed to them about food, but in different ways: for to the apostles, as being more capable, he sets forth the explanation at once without any wrapping of words; but the woman, as being less capable, he leads through many words to the knowledge of the truth. Now this that he says, "My food is to do the will of him who sent me, that I may perfect his work," has a sufficiently reasonable cause. For just as bodily food sustains man and perfects him, so that is the spiritual food of the soul and of the rational creature by which it is sustained and perfected. Now this consists in being joined to its end and in following the higher rule; which David, understanding this, said in Psalm 72:27: "But it is good for me to adhere to God." And therefore Christ, according as he is man, fittingly says that his food is to do the will of God, and to perfect his work. And these two indeed can be understood as one, yet in such a way that the second is the explanation of the first. Or they can be understood as one thing and another. If, however, they are understood as one, then the sense is: "My food is" — that is, in this is my firmness and sustenance — "that I do the will of him who sent me," according to that word of Psalm 39:9: "I have desired to do your will, O my God, and your law in the midst of my heart"; and below, John 6:38: "I came down from heaven, not to do my own will, but the will of him who sent me." But because "to do someone's will" is understood in two ways: in one way, that one causes him to will something; in another way, that one fulfills in deed what one knows him to will; therefore the Lord, explaining what it is to do the will of him who sent him, says that this, namely, is "that I may perfect his work," that is, that I may complete the works which I know him to will; below, John 9:4: "I must work the works of him who sent me while it is day." But if it is understood as one thing and another, then it should be known that Christ did two things in this world. First, he taught the truth, inviting and calling to faith, and in this he fulfilled the will of the Father; below, John 6:40: "This is the will of the Father who sent me, that everyone who sees the Son and believes in him may have eternal life." Second, he consummated the truth itself, opening in us, through his passion, the gate of life, giving the power of arriving at the consummated truth; below, John 17:4: "I have finished the work which you gave me to do." Thus, therefore, he says "My food is that I do the will of him who sent me," by calling men to the faith, "that I may perfect his work," by leading them to perfection. Or, according to Origen, every man who acts well ought to direct his intention to two things, namely to the honor of God and to the benefit of neighbor: because, as it is said in 1 Timothy 1:5, "the end of the commandment is charity," which contains the love of God and of neighbor. And thus, when we do something for the sake of God, the end of the commandment is God; but when for the benefit of neighbor, the end of the commandment is the neighbor. According to this, then, Christ says "My food is that I do the will of God," that is, that I direct and regulate my intention in those things which pertain to the honor of God; "that I may perfect his work," that is, that I do those things which pertain to the benefit and perfection of man. But against this: the works of God are perfect; therefore it is not fittingly said that the works of God are perfected. I respond that it must be said that among the other lower creatures man is a special work of God, because God made him to his image and likeness, Genesis 1:26. And this work was indeed perfect in the beginning, because God made man upright, as it is said in Ecclesiastes 7:30. Afterward, however, through sin he lost this perfection, and departed from uprightness. And therefore, in order that this work of the Lord might be perfect, it needed to be repaired; and this indeed was perfected through Christ, because it is said in Romans 5:19: "For as by the disobedience of one man many were made sinners, so by the obedience of one many will be made just." Thus Christ says "that I may perfect his work," that is, that I may bring man to perfection. Consequently, when he says, "Do you not say that there are yet four months, and then the harvest comes?" etc., he sets forth a comparison. But note that Christ asked the woman for drink, saying, "Give me to drink," and therefore on the occasion of this request he introduced the comparison about water. Here, however, the disciples urge the Lord to eat; hence also on the occasion of this the Lord introduces the comparison about spiritual food, because the same thing is understood by food and drink. Thus, therefore, there are some from whom God asks drink, as from the woman; but some offer drink to God. But no one offers food to God unless God has first asked it of him; for then do we offer spiritual food to God, when we beg from him our salvation, namely when we ask: "Your will be done, as in heaven, so on earth." We cannot obtain salvation from ourselves unless we are anticipated by prevenient grace, according to that word of Lamentations, last chapter, 21: "Convert us, O Lord, to you, and we shall be converted." He himself, therefore, asks first, who through prevenient grace makes us ask. Now in this comparison he first treats of the harvest; second, of the reapers, at the place: "And he who reaps receives a wage." Concerning the first he does two things. First he sets forth the comparison about the bodily harvest; second, about the spiritual harvest, at the place: "Behold I say to you, lift up your eyes," and so forth. Now by this that he says, "Do you not say that there are yet four months, and the harvest comes?" it is given to be understood that Christ withdrew from Judea immediately after the seizure of John, as is said in Matthew 4:12, and passed through Samaria; and that this was in winter, and John was likewise seized. Hence, because there the harvests are completed more promptly, there were four months from that time until the harvest. He says therefore "Do you not say," speaking of the bodily harvest, "that there are yet four months" remaining to come, "and the harvest comes"? That is, the time of the gathering of harvests. But "behold I say to you," speaking of the spiritual harvest, "lift up your eyes, and see the regions, that they are already white for the harvest." Here it should be known that the time of harvests is called the time of the gathering of fruits, and therefore every gathering of fruits is compared to the time of harvests. Now the time of the gathering of fruits is twofold. For nothing prevents, in temporal things as in spiritual things, that what is fruit with respect to the things preceding should also be seed with respect to the things following: for good works are the fruit of spiritual doctrine, such as faith and the like, which, however, are the seeds of eternal life, because through them one arrives at eternal life. Ecclesiasticus 24:23, wisdom says: "My flowers," with respect to the fruit following, "are the fruit of honor and of honesty," with respect to the things preceding. According to this, then, one gathering of the spiritual harvest is with respect to eternal fruits, namely the gathering of the faithful into eternal life, concerning which it is said in Matthew 13:39: "The harvest is the consummation of the world." And of this one it is not treated here. The other is in the present. And this can be understood in two ways. In one way, as the gathering of fruits, namely the conversion of the faithful who are to be gathered into the Church; in another way, as the very knowledge of truth, by which someone gathers the fruit of truth in his own soul: and of both, according to different expositions, it is treated here. Of the first, according to Augustine and Chrysostom, in this way: "you say" that it is not yet the time of the bodily harvest; but it is not so with the spiritual harvest — rather, "behold I say to you, lift up your eyes," namely, the eyes of the mind through consideration, or even the eyes of the body, "and see the regions, that they are already white for the harvest": because, namely, the whole region was full of Samaritans going out to Christ. Now this that he says, "they are white," is metaphorical; for when the crops have whitened, it is a sign that they are prepared for the harvest. He wished to signify nothing else by this than that men were prepared for him unto salvation and the reception of the word. Hence he says "see the regions," because not only the Jews, but also the Gentiles are prepared for the faith. Matthew 9:37: "The harvest indeed is great, but the laborers are few." And just as harvests are whitened on account of the presence of the sun, more burning in the summer season, so also men, through the coming of the sun of justice, namely Christ, and through his preaching and power, were being prepared for salvation. And of this sun it is said in Malachi 4:2: "To you who fear my name shall the sun of justice arise." And hence it is that the time of his coming is called the time of fullness; Galatians 4:4: "When, therefore, the fullness of time came, God sent his Son." Concerning the second gathering of the harvest, that is, of truth in the soul, Origen expounds, who says that one gathers as many fruits of truth in the harvest as truths he comes to know. And he holds that this whole passage which is said, "Do you not say that there are yet four months and the harvest comes? And behold I say to you: lift up your eyes and see the regions, that they are already white for the harvest," should be understood as spoken parabolically. And according to this, the Lord does two things in these words. First, he sets forth the false opinion of certain people; second, he excludes it, at the place: "I say to you." For the opinion of certain people was that no truth about any matter could be had by man, and from this was derived the heresy of the Academics, who said that nothing can be known for certain in this life; according to which it is said in Ecclesiastes 7:24: "I have tried all things in wisdom. I said: I will be wise. And it departed from me much further than it was." This opinion, therefore, the Lord touches upon, saying "Do you not say that there are yet four months, and the harvest comes?" That is, the whole of the present life, in which man serves the four elements, must come to an end so that after it the gathering of truth may be had in another life. But this opinion he consequently excludes when he says: it is not so; "but behold I say to you: lift up your eyes." For this is customarily said in sacred Scripture whenever something subtle and lofty is commanded to be considered, Isaiah 40:26: "Lift up your eyes on high, and see who created these things." For eyes, when they are not raised up from earthly things, or from carnal concupiscence, are not fit for the knowledge of spiritual fruit; for sometimes they are pressed down to earthly things, withdrawn from the consideration of divine things, according to that word of Psalm 16:11: "They have set their eyes to bend down to the earth"; sometimes they are blinded through concupiscence, Daniel 13:9: "And they turned away their eyes, that they might not look to heaven, nor remember the judgments of God." He says therefore, "lift up your eyes, and see the regions, that they are already white for the harvest," that is, so disposed that from them the truth can be known: for by "regions" are especially understood all the things from which truth can be received. And these especially are the Scriptures. Below, John 5:39: "Search the Scriptures... for they bear witness of me." And these regions did indeed exist in the Old Testament; but they were not white for the harvest, because men could not receive from them spiritual fruit until Christ came, who whitened them, opening their understanding; Luke, last chapter, 45: "He opened their mind, that they might understand the Scriptures." Likewise, the creatures are harvests, from which the fruit of truth is gathered; Romans 1:20: "The invisible things of God are clearly seen, being understood by the things that are made." But nevertheless the Gentiles who pressed after knowledge of them gathered from them rather the fruit of error than of truth, because, as it is said in the same place, "they served the creature rather than the creator." And therefore they were not yet white; but with Christ coming, they were made white for the harvest. Consequently, when he says, "and he who reaps receives a wage," he treats of the reapers; and concerning this he first sets forth the reward of the reapers; second he introduces a proverb, at the place: "for in this the word is true"; third he expounds, that is, applies it, at the place: "I sent you to reap." As to the first, it should be noted that the Lord, in expounding above what he had said about the spiritual water, set forth a condition by which the spiritual water differs from the bodily: namely, that whoever drinks of bodily water will thirst again, but whoever drinks of spiritual water will not thirst forever. In the same way also here, in expounding what he says about the harvest, he sets forth what is dissimilar between the bodily and spiritual harvest; hence he sets forth three things. One indeed according to which the likeness of each harvest is observed, namely that he who reaps, both in the bodily harvest and in the spiritual, receives a wage. Now he reaps spiritually who gathers the faithful into the Church, or who gathers the fruits of truth in his own soul. And each receives a wage, according to that word of 1 Corinthians 3:8: "Each one will receive his own wage according to his own labor." He sets forth two other things, according to which dissimilarity is observed. First indeed, that the fruit of the reaper who reaps the bodily harvest pertains to bodily life; but the fruit of him who reaps the spiritual harvest pertains to eternal life. And therefore he says "and he gathers," namely he who reaps spiritually, "fruit unto eternal life," namely the faithful who will have arrived at eternal life; Romans 6:22: "You have your fruit unto sanctification, and the end, life everlasting." Or, the very knowledge and exposition of truth by which man acquires eternal life. Ecclesiasticus 24:31: "They who explain me shall have life everlasting." Second, the dissimilarity is observed in this: that in the bodily harvest it is reckoned a misery that one should sow and another reap, hence he who sows is saddened by this, that another reaps; but with spiritual seed it is otherwise, because "he who sows rejoices together, and he who reaps." And indeed, according to Chrysostom and Augustine, those who sow the spiritual seed are the fathers of the Old Testament and the prophets; for, as it is said in Luke 8:11, "the seed is the word of God," which Moses and the prophets sowed in Judea; but the apostles reaped, because what they themselves intended, namely to bring men to Christ, they were not able to bring about, which nevertheless the apostles did. And therefore both rejoice together, namely the apostles and the prophets, in one dwelling place of glory, over the conversion of the faithful; Isaiah 51:3: "Joy and gladness shall be found therein, thanksgiving and the voice of praise." And by this the heresy of the Manichaeans, who condemn the fathers of the Old Testament, is refuted; since nevertheless, as the Lord here says, they will rejoice together with the apostles. According to Origen, however, those are called sowers in any discipline who hand down whatever principles of that discipline; but reapers are those who proceed further from them: and this all the more in this discipline, which is the science of all sciences. The prophets are sowers, because they handed down many things about divine matters; but the reapers are the apostles, who revealed by preaching and teaching those things which the prophets did not manifest to men. Ephesians 3:5: "which in other generations was not known... as it has now been revealed to his holy apostles." Consequently, when he says, "for in this the word is true," etc., a proverb is introduced; as if he should say, that "in this," that is, in this deed, "the word is true," that is, the common proverb is fulfilled, which existed among the Jews, namely "one sows and another reaps." This proverb seems to be derived from that which is said in Leviticus 26:16: "You shall sow the crop in vain, which shall be devoured by enemies." From which the Jews were accustomed, when someone labored at some matter and another rejoiced from it, to utter a proverb of this kind. This, then, is what the Lord says: in this, that the prophets sowed and labored, and you reap and rejoice, the proverb is fulfilled. Or otherwise: "In this the word is true," namely what I say, that one is he who sows, and another he who reaps; because you will reap the fruits from the labors of the prophets. But the prophets and the apostles are indeed distinct, not in faith — for both these and those had faith, Romans 3:21: "But now, without the law, the justice of God has been made manifest, testified to by the law and the prophets" — yet they are distinct in manner of life: because the prophets lived under the legal ceremonies, from which Christians and the apostles are free. Galatians 4:3-5: "And when we were children, we were serving under the elements of this world. But when the fullness of time came, God sent his Son, made of a woman, made under the law, that he might redeem those who were under the law, that we might receive the adoption of sons." And although the apostles and the prophets had labors of unequal time, nevertheless they will equally enjoy the joy together, and will receive a wage unto eternal life: "that he who sows and he who reaps may rejoice together." And this was prefigured in the Transfiguration of Christ, where all had their own glory — both the fathers of the Old Testament, namely Moses and Elijah, and the fathers of the New Testament, namely Peter, John, and James — giving us by this to understand that in that future glory the just of the New and of the Old Testament rejoice together. Consequently, when he says, "I sent you to reap that which you did not labor for," he adapts the proverb to the matter at hand, and first he says that the apostles are reapers; second he shows that they are laborers, at the place: "others have labored, and you have entered into their labors." As to the first, he says: I say that one is he who reaps — because you are the reapers — and another is he who sows — because I sent you to reap that which you did not labor for. He does not say "I will send" but "I sent," because he sent them twice: once before his passion, to the Jews, when he said to them: "Do not go into the way of the Gentiles... but go rather to the lost sheep of the house of Israel," as it is said in Matthew 10:5. And as to this mission, they were sent to reap that which they had not labored for, namely to convert the Jews themselves, among whom the prophets had labored. But he sent them after the resurrection to the Gentiles, saying to them, Mark, last chapter, 15: "Going into the whole world, preach the Gospel to every creature." In this mission they were sent to sow anew; hence the Apostle, Romans 15:20-21: "And so I have preached this Gospel, not where Christ was named, lest I should build upon another man's foundation; but as it is written: They to whom he was not spoken of shall see, and they that have not heard shall understand." And therefore he says "I sent," having regard to the first mission. Thus, therefore, the apostles are the reapers, but the others, namely the prophets, are the sowers. Hence he says "others have labored," by sowing the first beginnings of the doctrine of Christ, "and you have entered into their labors," to gather the fruits. Wisdom 3:15: "The fruit of good labors is glorious." The prophets labored, I say, in order to bring men to Christ. Below, John 5:46: "If you believed Moses, you would perhaps believe me also; for he wrote of me. But if you do not believe his writings, how will you believe my words?" But they themselves did not reap the fruit. Hence, according to this, Isaiah 49:4 said: "I have labored in vain, and without cause: I have consumed my strength for nothing."”

Post-Reformation

c. 1650 – 1900
1771
A.D.
John Gill Reformed
1697–1771
“I sent you to reap,.... To preach the Gospel, and gather in souls by your ministry; referring to the mission of them in Mat 10:6; that whereon ye bestowed no labour; being sent to the Jews, who had the writings of the prophets, and were versed in them; and had learned from them that the Messiah was to come, and were now in general expectation of him; so that they had nothing more to do, than to declare to those persons who were cultivated by the prophets, and were like to ground tilled and manured, that the Messiah was come, and the kingdom of heaven was at hand. Other men laboured; the prophets, and John the Baptist: and ye are entered into their labours; to finish the work they had begun, and which was almost done to their hands.”
Source
1849
A.D.
1774–1849
“By these words our Saviour testifies to his disciples, that the prophets had sown the seed in order to bring men to believe in Christ. This was the end of the law, this the fruit which the prophets looked for to crown their labours. He likewise shews that he himself that sent them, likewise sent the prophets before them; and that the Old and New Testament are of the same origin, and have the same design. (St. Chrysostom in St. Thomas Aquinas)”
Source
1871
A.D.
1871
“I sent you, &c.--The I is emphatic--I, the Lord of the whole harvest: "sent you," points to their past appointment to the apostleship, though it has reference only to their future discharge of it, for they had nothing to do with the present ingathering of the Sycharites. ye bestowed no labour--meaning that much of their future success would arise from the preparation already made for them. (See on Joh 4:42). others laboured--Referring to the Old Testament laborers, the Baptist, and by implication Himself, though He studiously keeps this in the background, that the line of distinction between Himself and all His servants might not be lost sight of. "Christ represents Himself as the Husbandman [rather the Lord of the laborers], who has the direction both of the sowing and of the harvest, who commissions all the agents--those of the Old Testament as well as of the New--and therefore does not stand on a level with either the sowers or the reapers" [OLSHAUSEN].”
Source
Modern · 1953 →

The in-app commentary runs from the Fathers to the early-modern record, then stops — that's where the public-domain sources end, not where the reading does. For the modern reading, follow the sources directly.