The interpretation timeline
1 John 3:16 Douay-Rheims

In this we have known the charity of God, because he hath laid down his life for us: and we ought to lay down our lives for the brethren.

A.D. 215 – 1871 7 witnesses 10 excerpts

Patristic

before A.D. 750
215
A.D.
c. A.D. 150–215
“"For He Himself laid down His life for us;" that is, for those who believe; that is, for the apostles. If then He laid down His life for the apostles, he means His apostles themselves: us if he said, We, I say, the apostles, for whom He laid down His life, "ought to lay down our lives for the brethren;" for the salvation of their neighbours was the glory of the apostles.”
Source
220
A.D.
Tertullian Patristic
c. A.D. 150–220
“John tells us that we must be ready to lay down our lives for our friends. If that is true, how much more should we be ready to lay them down for Christ?”
“John, in fact, exhorts us to lay down our lives even for our brethren, affirming that there is no fear in love: "For perfect love casteth out fear, since fear has punishment; and he who fears is not perfect in love.”
“And among these he notes the shield too, that ye may be able to quench the darts of the devil, when doubtless ye resist him, and sustain his assaults in their utmost force. Accordingly John also teaches that we must lay down our lives for the brethren; much more, then, we must do it for the Lord.”
430
A.D.
Augustine of Hippo Patristic
A.D. 354–430
“We have been given the privilege of being able to lay down our lives for our brothers. But are you prepared to die for Christ?”
“"In this know we love:" he means, perfection of love, that perfection which we have bidden you lay to heart: "In this know we love, that He laid down His life for us: and we ought to lay down our lives for the brethren." Lo here, whence that came: "Peter, lovest thou me? Feed My sheep." For, that ye may know that He would have His sheep to be so fed by him, as that he should lay down his life for the sheep, straightway said He this to him: "When thou wast young, thou girdedst thyself, and walkedst whither thou wouldest: but when thou shalt be old, thou shalt stretch forth thy hands, and another shall gird thee, and carry thee whither thou wouldest not. This spake He," saith the evangelist, "Signifying by what death he should glorify God;" so that to whom He had said, "Feed my sheep," the same He might teach to lay down his life for His sheep. Whence beginneth charity, brethren? Attend a little: to what it is perfected, ye have heard; the very end of it, and the very measure of it is what the Lord hath put before us in the Gospel: "Greater love hath no man," saith He, "than that one lay down his life for his friends." Its perfection, therefore, He hath put before us in the Gospel, and here also it is its perfection that is put before us: but ye ask yourselves, and say to yourselves, When shall it be possible for us to have this charity? Do not too soon despair of thyself. Haply, it is born and is not yet perfect; nourish it, that it be not choked.”
Source

Post-Reformation

c. 1650 – 1900
1771
A.D.
John Gill Reformed
1697–1771
“But whoso hath this world's good,.... The possessions of this world, worldly substance, the temporal good things of it; for there are some things in it, which are honestly, pleasantly, and profitably good, when used lawfully, and not abused, otherwise they are to the owner's hurt: or "the living of this world"; that which the men of the world give up themselves to, are bent upon, and pursue after; or on which men live, and by which life is maintained, and preserved, and made comfortable in the present state of things; such as meat, drink, apparel, money, houses, lands, &c. The Ethiopic version renders it, "he that hath the government of this world"; as if it pointed at a person that is in some high office of worldly honour and profit, and is both great and rich; but the words are not to be restrained to such an one only, but refer to any man that has any share of the outward enjoyments of life; that has not only a competency for himself and family, but something to spare, and especially that has an affluence of worldly substance; but of him that has not, it is not required; for what a man distributes ought to be his own, and not another's, and in proportion to what he has, or according to his ability: and seeth his brother have need; meaning, not merely a brother in that strict and natural relation, or bond of consanguinity; though such an one in distress ought to be, in the first place, regarded, for no man should hide himself from, overlook and neglect his own flesh and blood; but any, and every man, "his neighbour", as the Ethiopic version reads, whom he ought to love as himself; and especially a brother in a spiritual relation, or one that is of the household of faith: if he has need; that is, is naked and destitute of daily food, has not the common supplies of life, and what nature requires; and also, whose circumstances are low and mean, though not reduced to the utmost extremity; and if he sees him in this distress with his own eyes, or if he knows it, hears of it, and is made acquainted with it, otherwise he cannot be blameworthy for not relieving him. And shutteth up his bowels of compassion from him; hardens his heart, turns away his eyes, and shuts his hand; has no tenderness in him for, nor sympathy with his distressed brother, nor gives him any succour: and this shows, that when relief is given, it should be not in a morose and churlish manner, with reflection and reproach, but with affection and pity; and where there is neither one nor the other, how dwelleth the love of God in him? neither the love with which God loves men; for if this was shed abroad in him, and had a place, and dwelt in him, and he was properly affected with it, it would warm his heart, and loosen his affections, and cause his bowels to move to his poor brother: nor the love with which God is loved; for if he does not love his brother whom he sees in distress, how should he love the invisible God? Jo1 4:20; nor that love which God requires of him, which is to love his neighbour as himself.”
Source
1832
A.D.
Adam Clarke Methodist
1762–1832
“Hereby perceive we the love of God - This sixteenth verse of this third chapter of John's first epistle is, in the main, an exact counterpart of the sixteenth verse of the third chapter of St. John's gospel: God so loved the world, that he gave his only-begotten Son, etc. Here the apostle says, We perceive, εγνωκαμεν, we have known, the love of God, because he laid down his life for us. Of God is not in the text, but it is preserved in one MS., and in two or three of the versions; but though this does not establish its authenticity, yet του Θεου, of God, is necessarily understood, or του Χριστου, of Christ, as Erpen's Arabic has it; or αυτου εις ἡμας, his love to us, as is found in the Syriac. A higher proof than this of his love Christ could not have possibly given to the children of men. We ought to lay down our lives for the brethren - We should risk our life to save the lives of others; and we should be ready to lay down our lives to redeem their souls when this may appear to be a means of leading them to God.”
Source
1849
A.D.
1774–1849
“The charity of God, [2] because he hath laid down his life for us. Jesus Christ, therefore, who laid down his life for us, was God. It is true at present the words of God are wanting in most Greek manuscripts: yet the Protestant translation has them. (Witham)”
1871
A.D.
1871
“What true love to the brethren is, illustrated by the love of Christ to us. Hereby--Greek, "Herein." the love of God--The words "of God" are not in the original. Translate, "We arrive at the knowledge of love"; we apprehend what true love is. he--Christ. and we--on our part, if absolutely needed for the glory of God, the good of the Church, or the salvation of a brother. lives--Christ alone laid down His one life for us all; we ought to lay down our lives severally for the lives of the brethren; if not actually, at least virtually, by giving our time, care, labors, prayers, substance: Non nobis, sed omnibus. Our life ought not to be dearer to us than God's own Son was to Him. The apostles and martyrs acted on this principle.”
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.