The interpretation timeline
Matthew 9:36 Douay-Rheims

And seeing the multitudes, he had compassion on them: because they were distressed, and lying like sheep that have no shepherd.

A.D. 367 – 1871 9 witnesses 20 excerpts

Patristic

before A.D. 750
367
A.D.
Hilary of Poitiers Patristic
c. A.D. 310–367
“Figuratively; When salvation was given to the Gentiles, then all cities and towns were enlightened by the power and entrance of Christ, and escaped every former sickness and infirmity. The Lord pities the people troubled with the violence of the unclean Spirit, and sick under the burden of the Law, and having no shepherd at hand to bestow on them the guardianship of the Holy Spirit. But of that gift there was a most abundant fruit, whose plenty far exceeded the multitude of those that drank thereof; how many soever take of it, yet an inexhaustible supply remains; and because it is profitable that there should be many to minister it, He bids us ask the Lord of the harvest, that God would provide a supply of reapers for the ministration of that gift of the Holy Spirit which was made ready; for by prayer this gift is poured out upon us from God.”
Source
407
A.D.
John Chrysostom Patristic
A.D. 347–407
“The Lord would refute by actions the charge of the Pharisees, who said, He casteth out dæmons by the Prince of the dæmons; for a dæmon having suffered rebuke, does not return good but evil to those who have not shewn him honour. But the Lord on the other hand, when He has suffered blasphemy and contumely, not only does not punish, but does not utter a hard speech, yea He shews kindness to them that did it, as it here follows, And Jesus went about all their towns and villages. Herein He teaches us not to return accusations to them that accuse us, but kindness. For he that ceases to do good because of accusation, shews that his good has been done because of men. But if for God’s sake you do good to your fellow-servants, you will not cease from doing good whatever they do, that your reward may be greater.”
Source
“Nor does Christ’s goodness rest here, but He manifests His care for them, opening the bowels of His mercy towards them; whence it follows, And seeing the multitudes, he had compassion upon them.”
“This is an accusation against the rulers of the Jews, that being shepherds they appeared like wolves; not only not improving the multitude, but hindering their progress. For when the multitude marvelled and said, It was never so seen in Israel, these opposed themselves, saying, He casteth out dæmons by the prince of the dæmons. (vid. Ps. 102:19.)”
Source
“He shews us that it is a great gift that one should have the power of rightly preaching, in that He tells them that they ought to pray for it. Also we are here reminded of the words of John concerning the threshing-floor, and the fan, the chaff, and the wheat.”
420
A.D.
Jerome Patristic
c. A.D. 347–420
“Observe how equally in villages, cities, and towns, that is to great as well as small, He preaches the Gospel, not respecting the might of the noble, but the salvation of those that believe. It follows, Teaching in their synagogues; this was His meat, going about to do the will of His Father, and saving by His teaching such as yet believed not.”
Source
“He first preached and taught, and then proceeded to heal sicknesses, that the works might convince those who would not believe the words. Hence it follows, Healing every sickness and every disease, for to Him alone nothing is impossible.”
“The great harvest denotes the multitude of the people; the few labourers, the want of instructors.”

Medieval

c. 750 – 1100
908
A.D.
c. A.D. 841–908
“Understand, ‘of God;’ for though temporal blessings are also proclaimed, yet they are not called The Gospel. Hence the Law was not called a Gospel, because to such as kept it, it held out not heavenly, but earthly, goods.”
“It should be known that those whom He healed outwardly in their bodies, He also healed inwardly in their souls. Others cannot do this of their own power, but can by God’s grace.”
“Herein Christ shews in Himself the disposition of the good shepherd and not that of the hireling. Why He pitied them is added, Because they were troubled1, and sick1 as sheep that have no shepherd—troubled either by dæmons, or by divers sicknesses and infirmities.”
“Or, He then increased their number when He chose the seventy and two, and then when many preachers were made what time the Holy Spirit descended upon the believers.”

Scholastic

c. 1100 – 1500
1256
A.D.
Thomas Aquinas Catholic
1225–1274
“It has been shown how he came to the aid of those who met him; here he touches on the fact that he went to them. And here he touches on two things: first, how he bestowed a certain effect on some; second, how he bestowed affection, at the place, "But seeing the crowds, he had compassion on them." And concerning the first, he shows first where he bestowed help; second, what he taught; third, what he did. He says therefore, "And Jesus went about all the cities and villages." In this an example is given to preachers, that they should not be content to preach in one place only; John 15:16: "I have appointed you, that you should go and bring forth fruit," etc. "All the cities and villages." And this is well ordered with what precedes. For they had said that he cast out devils by the prince of devils; therefore he shows that he does not have a devil, so that it may fit him, Psalm 119:7: "With them that hated peace I was peaceable; when I spoke to them, they fought against me without cause." There follows what he was proclaiming; for he was doing two things, because in the synagogues he was teaching and preaching: teaching the things that pertain to faith, preaching the things that pertain to morals. Likewise before many, because in the synagogues; Psalm 39:10: "I have declared thy justice in a great church" — in which also it differs from the teaching of heretics, which is in secret. Otherwise is the teaching of Christ; John 18:20: "I have spoken nothing in secret to you." Likewise he touches on what he teaches, because "the Gospel of the kingdom"; John 18:37: "For this was I born, and for this I came into the world, that I should give testimony to the truth," etc. Whence he was teaching heavenly things; Isaiah 48:17: "I am the Lord thy God that teach thee profitable things." Afterward it is shown by the deed what he did, "curing every sickness and every infirmity." "Sicknesses," as to the grave infirmities; "infirmities," as to the light ones; Psalm 102:3: "Who forgiveth all thy iniquities, who healeth all thy diseases." And why this? That he might confirm by miracle what he said by word, as in Mark, the last chapter, 20: "the Lord working withal, and confirming the word with signs that followed." Likewise, that he might show an example to preachers, that they should both do and teach; Acts 1:1: "Jesus began to do and to teach." "And seeing the crowds, Jesus had compassion on them." Here he shows how the Lord bestowed affection on certain persons; and this against certain people, for there was an opinion that no affection sufficed, but effect was required; but here he says, "And seeing the crowds, Jesus had compassion on them." And first he touches on how he had compassion; second he gives an example. And first he sets forth the mercy of Christ; second, the cause. He says therefore "seeing," etc., namely by pious consideration, "he had compassion on them," because it is proper to him to have mercy; Psalm 144:9: "His tender mercies are over all his works." David desired this gaze, saying, Psalm 24:16: "Look thou upon me, and have mercy on me." And on whom he had mercy: because they were "vexed" — by devils — and likewise "lying" — that is, laid low by infirmities. Or: "vexed" by errors, "lying" in sins, "as sheep without a shepherd." Whence Proverbs 11:14: "Where there is no governor, the people shall fall," etc. And Ezekiel 34:5: "My sheep are scattered, because there was no shepherd for them"; and in the same chapter: "Woe to the shepherds of Israel who fed themselves." As Zechariah 11:17: "O shepherd and idol, that forsaketh the flock." "Then he saith to his disciples." Here he leads some to have mercy, and first he assigns the cause; second he leads to the effect, at the place, "Pray ye therefore the Lord of the harvest that he send forth laborers into his harvest." And he sets forth two causes: first, the multitude of those tending toward the good; second, the fewness of teachers, at the place, "but the laborers are few." Many had come together; therefore he says, "the harvest indeed is great." Harvest is not spoken of when the grain is flowering, or when it is in the ear, but then when it is already disposed to be gathered; thus men were already disposed to believe through the work of the preachers. The like is found in John 4:35: "Lift up your eyes, and see the countries, for they are white already to harvest." And "the laborers are few," namely the good ones; whence the Apostle, 1 Corinthians 3:9: "For we are God's coadjutors." Bestowing therefore what is yours to give. And what? "Pray the Lord of the harvest that he send laborers into his harvest." When we have a deficiency, we ought to have recourse to God, since the office of preaching is obtained only by prayers: for he who sends the laborers is the Lord, whence it is said, "I have sent you." And he asks to be asked, so that he may accumulate merit for us, while we pray for the salvation of others. Likewise he established such an order, that the holiness of some might profit others, as in 1 Peter 4:10: "As every man hath received grace, ministering the same one to another, as good stewards of the manifold grace of God," etc. Whence he wills that whatever of grace and holiness they have received, they should bestow on others, and he himself, being asked, hears them. For he asks that he himself be asked to send them; Romans 10:15: "How shall they preach unless they be sent?" For authority is thereby acquired; likewise grace, whence: "The charity of Christ presseth us." Likewise, "pray the Lord of the harvest that he send laborers" — not hirelings who corrupt by bad example — "into his harvest," namely into the harvest of God. For hirelings are not sent into the harvest of God, but into their own harvest, because they seek not the glory of God, but their own advantage.”
Source

Post-Reformation

c. 1650 – 1900
1771
A.D.
John Gill Reformed
1697–1771
“Pray ye therefore the Lord of the harvest,.... By "the Lord of the harvest" is either meant God the Father, whose are all the elect, who has a hearty concern for them, and will have them all gathered in, not one of them shall be left; or the Lord Jesus Christ himself, who has the care and charge of the whole election of grace; and who as he must, he will bring them all in; and who has power of sending forth labourers, as the following chapter shows; and so this is a proof of prayer being made to Christ; that he will send forth labourers into his harvest. This is the petition the disciples of Christ were put upon making to the Lord of the harvest, on consideration of the present condition multitudes of souls were in: they could not make, qualify, and send out ministers themselves; this is not man's work, but God's: he only is able to furnish with ministerial gifts, to work upon, and powerfully incline the hearts of men to this service, to call and send them forth into it, and to assist and succeed them in it. The persons desired to be sent are "labourers"; faithful, diligent, and industrious preachers of the Gospel; such as lay out themselves, their time, talents, and strength, in their master's service; and do not indulge themselves in sloth and idleness: the place they are desired to be sent into is, "into the harvest"; into the field of the world, where God's elect lie, and there labour in preaching the Gospel; hoping for a divine blessing, and an almighty power to attend their ministrations, for the conversion of sinners, and edification of saints. The request the disciples are directed to make, concerning these persons for this work, is, that the Lord of the harvest would "send", or "thrust" them "forth"; implying power and efficacy, and authority, on the part of the sender; and backwardness on the part of those that are sent, through modesty: a sense of the greatness of the work, and of their own unworthiness and unfitness for it. Very opportunely did our Lord move his disciples to put up this petition, and was done, no question, with a view to, and to prepare for, his mission of the twelve to preach the Gospel, of which there is an account in the next chapter. Next: Matthew Chapter 10”
Source
1849
A.D.
1774–1849
“He had compassion on them. The bowels of his compassion yearned to see multitudes cast down and oppressed, like sheep that are without a shepherd. The Pharisees indeed were their shepherds; but they acted the part of ravenous wolves, not only neglecting to lead the people to virtue, but even hindering, as much as they could, their advancement in good; for when the admiring multitude cried out, “Never did the like appear in Israel,” they immediately decried it, saying, “By the prince of devils he casteth out devils.” (St. Chrysostom, hom. xxxiii.)”
Source
1871
A.D.
1871
“But when he saw the multitudes, he was moved with compassion on them, because they fainted--This reading, however, has hardly any authority at all. The true reading doubtless is, "were harassed." and were scattered abroad--rather, "lying about," "abandoned," or "neglected." as sheep, having no shepherd--their pitiable condition as wearied under bodily fatigue, a vast disorganized mass, being but a faint picture of their wretchedness as the victims of pharisaic guidance; their souls uncared for, yet drawn after and hanging upon Him. This moved the Redeemer's compassion.”
Source

Undated

date unknown
date
unknown
Glossa Ordinaria Medieval
“(non occ.) He taught in their synagogues the Gospel of the Kingdom, as it follows, Preaching the Gospel of the Kingdom.”
“(ap. Anselm.) By disease we may understand complaints of long standing, by sickness any lesser infirmity.”
“(ap. Anselm.) Or, troubled by dæmons, and sick, that is, benumbed and unable to rise; and though they had shepherds, yet they were as though they had them not.”
“(ap. Anselm.) The harvest are those men who can be reaped by the preachers, and separated from the number of the damned, as grain is beaten out from the chaff that it may be laid up in granaries.”
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.