John 13:34 (BSB)

A new commandment I give you: Love one another. As I have loved you, so you also must love one another.

From John 13. Also in the ESV.

Commentary on John 13:34

• John Calvin (Reformed), Calvin's Commentaries on John 13:34: 34. A new commandment I give you. To the consolation he adds an exhortation, that they should love one another; as if he had said, “Yet while I am absent from you in body, testify, by mutual love, that I have not taught you in vain; let this be your constant study, your chief meditation.” Why does he call it a new commandment? All are not agreed on this point.
• Matthew Henry (Presbyterian), Matthew Henry's Complete Commentary on John 13:31-35: This and what follows, to the end of ch. 14, was Christ's table-talk with his disciples. When supper was done, Judas went out; but what did the Master and his disciples do, whom he left sitting at table? They applied themselves to profitable discourse, to teach us as much as we can to make conversation with our friends at table serviceable to religion. Christ begins this discourse.
• John Gill (Reformed Baptist), Exposition of the Old and New Testaments on John 13:34: A new commandment I give unto you,.... As parents, when they take their leave of their children, in their dying moments, give them proper instructions and orders, and lay their dying injunctions on them, so Christ taking his leave of his disciples, gives them his; which were, that they love one another: as brethren in the same family, children of the same Father, and fellow...
• Albert Barnes (Presbyterian), Barnes' New Testament Notes on John 13:34: Verse 34. A new commandment. This command he gave them as he was about to leave them, to be a badge of discipleship, by which they might be known as his friends and followers, and by which they might be distinguished from all others.