The interpretation timeline
Joel 2:13 Douay-Rheims

And rend your hearts, and not your garments, and turn to the Lord your God: for he is gracious and merciful, patient and rich in mercy, and ready to repent of the evil.

A.D. 258 – 1871 5 witnesses

Patristic

before A.D. 750
258
A.D.
Cyprian Patristic
c. A.D. 200–258
“Let each one confess his sin, I beseech you, brethren, while he who has sinned is still in this world, while his confession can be admitted, while the satisfaction and remission effected through the priest is pleasing with the Lord. Let us turn to the Lord with our whole mind, and, expressing repentance for our sin with true grief, let us implore God's mercy. Let the soul prostrate itself before him; let sorrow give satisfaction to him; let our every hope rest upon him. He himself tells how we ought to ask. He says, "Return to me with all your hearts, in fasting and in weeping, and in mourning, and rend your hearts, not your garments." Let us return to the Lord with a whole heart; let us placate his wrath and displeasure by fastings, weepings and mournings, as he himself admonishes.”
Source

Scholastic

c. 1100 – 1500
1105
A.D.
Rashi Jewish
1040–1105
“and not your garments—for I do not pay heed to the rending of your garments. Another explanation: Rend your hearts and you will not need to rend your garments because of mourning. and He repents of the evil—I.e., He turns to another thought.”

Post-Reformation

c. 1650 – 1900
1771
A.D.
John Gill Reformed
1697–1771
“And rend your heart, and not your garments,.... Which latter used to be done in times of distress, either private or public, and as a token of grief and sorrow, Gen 37:34; nor was it criminal or unlawful, the apostles themselves used it, Act 14:14; nor is it absolutely forbidden here, only comparatively, that they should rend their hearts rather than their garments; or not their garments only, but their hearts also; in like sense as the words in Hos 6:6; are to be taken as rending garments was only an external token of sorrow and might be done hypocritically. Where no true repentance was, the Lord calls for that, rather than the other; and that they would show contrition of heart and brokenness of spirit under a sense of sin, and in the view of pardoning grace and mercy; which is here held forth, to influence godly sorrow and evangelical repentance; the acts of which, flowing from faith in Christ are much more acceptable to the Lord than any outward expressions of grief; see Psa 51:17. The Targum is, "remove the wickedness of your heart but not with the rending of your meats;'' the rending of the garment goes to the heart some say to the navel (w): and turn unto the Lord your God; consider him not as an absolute God, and as an angry one, wrathful and inexorable; but as your covenant God and Father as your God in Christ, ready to receive backsliding sinners and prodigal sons; yea all sinners sensible of sin that flee to him for mercy through Christ: for be is gracious and merciful; he is the God of all grace, and has laid up a fulness of it in Christ; and he gives it freely to them that ask it of him without upbraiding them with their sins; he is rich and plenteous in mercy, and ready to forgive; be delights in showing mercy, and in them that hope in it; and this is no small encouragement to turn to the Lord, and seek mercy of him: and, besides, he is slow to anger; he is not hasty to stir it up, and show it; he bears with much longsuffering the vessels of wrath; and his longsuffering to his own people issues in their salvation: he waits to be gracious to them; and, though he may seem to be angry, he does not stir up all his wrath their sins deserve nor does he retain anger for ever: and of great kindness; both in a providential way, and in a way of special grace through Christ; whom he has provided as a Saviour, and sent him into the world as such, and saves sinners by obedience sufferings, and death: these characters of God are taken out of Exo 34:6; and are admirably adapted to engage and encourage sensible souls to turn to the Lord by acts of faith in him, and repentance towards him; see Isa 55:7; and it is added, and repenteth him of the evil; which the sins of men deserve; and he has threatened on account of them; not that he ever changes the counsels of his will, but alters the course of his providence, and the manner of his conduct towards men, according to his unalterable repentance otherwise does not properly belong to God, Num 23:19; but is ascribed to him after the manner of men; and is used to express his compassion men; how ready he is to receive and forgive returning sinners and not execute the threatened and deserved evil and to bestow all needful good; see Jon 3:10. The Targum is, "and he recalls his word from bringing on the evil.'' (w) T. Bab. Moed Katon, fol. 26. 2.”
Source
1849
A.D.
1774–1849
“Garments, as was customary in great distress. God will not be satisfied with mere external proofs of repentance. (Calmet) — Evil. He will forego his threats if we do penance. (St. Jerome) — He punishes unwillingly, Isaias xxviii. 21.”
1871
A.D.
1871
“Let there be the inward sorrow of heart, and not the mere outward manifestation of it by "rending the garment" (Jos 7:6). the evil--the calamity which He had threatened against the impenitent.”
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.