I am the Lord who search the heart and prove the reins: who give to every one according to his way, and according to the fruit of his devices.

“For such things as these serve for exercise and trial, so that, having proved ourselves zealous and chosen servants of Christ, we may be fellow heirs with the saints. For thus Job: "The whole world is a place of trial to people on the earth." Nevertheless, they are proved in this world by afflictions, labors and sorrows, to the end that each one may receive of God such reward as is appropriate for him, as he said by the prophet, "I am the LORD who tries the hearts and searches the reins, to give to everyone according to his ways."”

“That it belongs to God alone to know people's secrets, hear what the prophet says: "You alone know the heart," and again, "God examines the heart and the seat of emotions," and Jeremiah, too, says, "The heart is inscrutable above all things, and he is man, and who shall know him?" and, "People shall look on the face but God on the heart."”

“"And Thou shalt direct the righteous, O God, who searcheth the hearts and reins." How then can the righteous be directed but in secret? ...How then is the righteous man directed in so great confusion of pretence, save whilst God searcheth the hearts and reins; seeing all men's thoughts, which are meant by the word heart; and their delights, which are understood by the word reins? ...God then, searching our heart, and perceiving that it is there where our treasure is, that is, in heaven; searching also the reins, and perceiving that we do not assent to flesh and blood, but delight ourselves in the Lord, directs the righteous man in his inward conscience before Him, where no man seeth, but He alone who perceiveth what each man thinketh, and what delighteth each. For delight is the end of care; because to this end does each man strive by care and thought, that he may attain to his delight. He therefore seeth our cares, who searcheth the heart. He seeth too the ends of cares, that is delights, who narrowly searcheth the reins; that when He shall find that our cares incline neither to the lust of the flesh, nor to the lust of the eyes, nor to the pride of life, all which pass away as a shadow, but that they are raised upward to the joys of things eternal, which are spoilt by no change, He may direct the righteous, even He, the God who searcheth the hearts and reins. For our works, which we do in deeds and words, may be known unto men; but with what mind they are done, and to what end we would attain by means of them, He alone knoweth, the God who searcheth the hearts and reins.”

“Here the obstinacy of the people is shown explicitly, which is the cause of their reprobation: hence first he shows their obstinate malice; second, the consummated punishment, ch. 19: Thus says the Lord, etc. In the first, two parts. In the first, the causes of the obstinacy are set down; second, the obstinacy itself is proved through experience, ch. 18: The word that was made to Jeremiah from the Lord. The first into two. In the first he sets down the causes of the obstinacy, in the second he calls them back to the worship of their former religion, there: Thus says the Lord, etc. Concerning the first, two parts. First he touches on one cause, namely the affection of iniquity, setting down the fault, in which he sets down the example: the sin of Judah, of the two tribes, is written — that is, so deeply impressed upon their affection, especially of idolatry — as a writing that is made with an iron stylus, upon the nail, that is, upon the adamant, which is a stone polished after the manner of a nail. Zach. 7: They set their heart as an adamant, lest they should hear the law, and the words which the Lord of hosts sent in his holy spirit by the hand of the former prophets. Or, sin, that is, the sentence for the sin. And he expounds the affection of the sin: engraved, that is, driven deep, upon the breadth, that is, upon the heart dilated in the affection of sin: hence the heart thus dilated stands in the place of the adamant, and the horns of the altars, that is, of the idols, stand in the place of the iron stylus. For God had commanded that four horns should go forth from the altar, on which the grating should hang, Exod. 27; and they had made the like on the altars of the idols. Hosea 8: Ephraim has multiplied altars to himself for sinning, altars have become to him unto sin. He also sets down a sign of this affection in the succession of offspring: when their children shall have remembered, retaining it in affection, in the diversity of place, of the altars which were built in the cities. Above, ch. 2: Under every leafy tree you lay prostrate, a harlot. And joining to it the punishment, namely the plundering of the goods which pertain to the necessity of life: your strength, that is, the goods in which you thought yourself to be strong, like sand, like camps. Above, ch. 15: Your riches, and treasures I will give up to plunder freely, in all your sins, and in all your borders. That is, when your malice shall have been so consummated that the children imitate the fathers, worshipping idols in all places, then I will give your strength, and all your treasures, up to plunder. And of the goods which pertain to the worship of idolatry: your high places, in which they worshipped idols. Ezek. 6: Behold I will bring a sword upon you, and I will destroy your high places, and I will demolish your altars, and your idols shall be broken, and I will cast down your slain before your idols. He also threatens captivity: you shall be left, O Jerusalem, from your inheritance, from the people subject to you. Or, O nation, from the land, while you shall go into captivity. Lam. 1: How does the city sit solitary that was full of people? She has become as a widow, the mistress of the nations; the princess of the provinces has become tributary. He threatens servitude too: and I will make you serve your enemies. Deut. 28: You shall serve your enemy, whom the Lord will send upon you, in hunger, and thirst, and nakedness, and in want of all things; and he will put an iron yoke upon your neck, until he consume you. And touching the proximate cause of the punishment, namely the divine wrath, which is the will to punish: because you have kindled a fire. Deut. 32: A fire is kindled in my fury, and shall burn even to the lowest depths of hell. Second, he touches on another cause, namely the confidence of impunity: cursed is the man who trusts in man. Now they promised themselves impunity on three grounds. First, from the power of their friends, namely the Egyptians: and this he removes first. Second, from the abundance of riches, and this, there: the partridge has hatched what she did not lay. Third, from disbelief in the divine threats; and this, there: behold they say to me, where is the word of the Lord? Concerning the first, two parts. First he sets down the distinction between those who trust in the Lord and in men; second he introduces the author of this distinction, there: the heart of man is perverse. Concerning the first, two parts. First is set down the curse of those who trust in human help, where he sets down the curse: cursed — as if given over to evil. And he sets down flesh as the arm, that is, strength; in which is set down the unreasonableness of the hope, because by flesh human frailty is signified. And he departs from the Lord; in which is shown the reason for the curse: for it is permitted to trust in man under God, but not so that God be forsaken. And this is said on account of the Jews, who, God being despised, placed their hope in the Egyptians. Isa. 31: Woe to them that go down into Egypt for help, trusting in horses, and putting their confidence in chariots, because they are many, and in horsemen, because they are very strong; and they have not trusted in the Holy One of Israel, and have not sought after the Lord. Ps. 145: Trust not in princes, in the sons of men, in whom there is no salvation. And he sets down a comparison for the curse: for he shall be like the tamarisk, which is held vile. Symmachus: like a fruitless tree in the wilderness. He shall not see: because before the deliverance from captivity, almost all had died. But he shall dwell; in which is shown the horror of the place of captivity — not that it was evil in itself, but to those who were oppressed in servitude — in drought, in the desert, which is not cultivated, but is of dry air, which makes the trees unfruitful; salt land, as to the dryness of the earth, from the parching of moisture by the sun. Ps. 106: He has turned rivers into a wilderness, and the springs of waters into thirst. Second is set down the blessing of those who trust in the divine help. And first he sets down the blessing: blessed is the man who trusts in the Lord, and the Lord shall be his confidence — namely, that in whatever he trusts, the reason for trusting is God. Ps. 2: When his wrath shall be kindled in a short time, blessed are all they that trust in him. Isa. 30: Blessed are all they that wait for him. Second he sets down a comparison taken from a tree — first as to the firmness of the roots: and he shall be like a tree, in which is figured the firmness of divine protection. Ps. 1: And he shall be like a tree which is planted near the running waters, which shall bring forth its fruit in due season. Second, as to the greenness of the leaves: and his leaf shall be — in which is signified temporal prosperity, and spiritual verdure. Prov. 11: The just shall spring up like a green leaf. Third, as to the abundance of the fruits, in which is signified the plenty of good works: nor shall it ever cease to bear fruit. Apoc. 21: yielding its fruit every month. And because the Jews could say that a distinction of rewards could not be made on account of the diversity of thoughts, therefore he consequently introduces the author of this distinction. And first he poses the question: it is perverse, that is, entangled with many evils. Prov. 20: As deep water, so is counsel in the heart of a man; but a wise man will draw it out. Second he sets down the response: and he sets down two things which make the distinction of judgment sufficient: namely knowledge: I the Lord searching the hearts — as to thoughts — and the reins — as to the affections. Rom. 8: He who searches the hearts knows what the Spirit desires, because he asks according to God for the saints. And justice: who give to each according to his way — as to the disposition of the heart — and his fruit — as to the outward work. Isa. 3: Say to the just man that it is well, for he shall eat the fruit of his devices.”

“I the Lord search the heart,.... The inward parts of it, every room and corner in it; and know the thoughts of it; all its intents, purposes, designs, contrivances, and imaginations; all the secret motions of it, and the wickedness that is in it; so that this is an answer to the question in the preceding verse; and therefore, though the heart is deceitful, it cannot deceive him, because he judges not according to outward appearance; he sees and knows the heart; and none but the Lord, or he who is Jehovah, can so search the heart as thus to know it; wherefore, since Christ is said to search the reins and the heart, and to know the thoughts of men, and to be a discerner of the thoughts and intents of the heart, he must be Jehovah, and the true God, Rev 2:23, I try the reins; the most inward and remote parts, covered with fat, and out of sight: these are the seat of the affections; and the Lord tries these, whether they are towards him or not; and whether sincere or hypocritical; Christ the omniscient God knew Peter's love to him, and the sincerity of it; for which he appeals to him as such, Joh 21:17, even to give every man accordions to his ways, and according to the fruit of his doings; to do which it is necessary to search the heart, and try the reins, the fountain of all actions; and in which the principles of them are, and according to which they are denominated and judged of: in the future judgment every secret thing will be brought into account; the counsels of the heart will be made manifest; the book of conscience will be opened; and out of it, as well as other books, men will be judged according to their ways and works; and therefore it is requisite that the Judge should be the Lord God omniscient, the searcher and trier of the hearts and reins, as Christ is.”