The interpretation of this verse largely depends on the meaning given to the καθὼς, if, as many translate it, "even as I loved you;" or, "after the manner and type of my love to you;" then an amply sufficient explanation arises of the novelty of the ἐντολή. So new a type of love is given that, as the Greek expositors generally have urged, there is a deeper intensity in the love than can be found in the Mosaic principle, Love thy neighbor as thyself." In this commandment, which embraces the whole law, self-love is assumed, and is made the standard for the love of neighbor. This ἐντολή, on the other hand, would be based on a new principle, and measured by a higher standard, and even mean more than love of self altogether. Christ's love to his disciples was self-abandoning, self-sacrificing love. Pulpit Commentary
They were to befriend each other in trials; be careful of each other's feelings and reputation; deny themselves to promote each other's welfare. See
1 John 3:23;
1 Thessalonians 4:9;
1 Peter 1:22;
2 Thessalonians 1:3;
Galatians 6:2;
2 Peter 1:7. In all these places the command of Jesus is repeated or referred to, and it shows that the first disciples considered this indeed as the special law of Christ. This command or law was, moreover, new in regard to the extent to which this love was to be carried; for he immediately adds, "As I have loved you, that ye also love one another." His love for them was strong, continued, unremitting, and he was now about to show his love for them in death.
John 15:13; "greater love hath no man than this, that a man lay down his life for his friends." So in
1 John 3:16 it is said that "we ought also to lay down our lives for the brethren." This was a new expression of love; and it showed the strength of attachment which we ought to have for Christians, and how ready we should be to endure hardships, to encounter dangers, and to practice self-denial, to benefit those for whom the Son of God laid down his life. Barnes
its a higher calling from Jesus in this passage than what is required in the law.