1 John 3:16

Hereby perceive we the love [of God]
The phrase "of God" is not in the Oriental versions, nor in the Greek copies, but is in the Complutensian edition, and in the Vulgate Latin version, and is favoured by the Syriac version, which reads, "by this we know his love to us"; and so the Ethiopic version, "by this we know his love". That is, the love of the Lord Jesus Christ, who is truly and properly God, the great God, the mighty God, the true God, and God over all, blessed for ever. His love is manifested to his people, and perceived by them in various instances; but in nothing is it more clearly seen than in the following one:

because he laid down his life for us:
of the life of Christ, and his laying it down in the room of his people, (See Gill on 15:13), which shows his love, his free grace and favour; for this arose not from any merit or worth in the persons he died for; not from their love, loveliness, or duty, but from his rich mercy, and the great love wherewith he loved them; and which, though it cannot be equalled, should be imitated:

and we ought to lay down [our] lives for the brethren:
not in such sense, or for such ends and purposes, as Christ laid down his life for us; for no man, as by giving his money, so by laying down his life, can redeem his brother, or give to God a ransom for him: but the meaning is, that saints ought to risk their lives, and expose themselves to dangers, for the sake of their brethren, when they are called to it, and the case requires it: as Priscilla and Aquila laid down their necks, or ventured their lives for the Apostle Paul, ( Romans 16:3 Romans 16:4 ) ; and they should also, when called unto it, freely lay down their lives in the cause of Christ, and for the sake of his Gospel, for the gaining of souls to Christ, and for the confirming of the faith of the brethren in him, as the apostles of Christ, and the martyrs of Jesus, have done; this is an argument for brotherly love, in the highest instance of it, taken from the example of our Lord Jesus Christ, than which nothing is more forcible, or can lay a greater obligation on the saints.