By this shall all men know that ye are my disciples, if ye have love one to another.

People's New Testament

13:35 By this shall all men know that ye are my disciples. The love and self-sacrifice of Christians has done more to extend the name of Christ than argument. In the early ages, heathen were wont to say: See how these Christians love one another.

Jamieson-Fausset-Brown Bible Commentary

35. By this shall all men know that ye are my disciples-the disciples of Him who laid down His life for those He loved.

if ye have love one to another-for My sake, and as one in Me; for to such love men outside the circle of believers know right well they are entire strangers. Alas, how little of it there is even within this circle!

Matthew Henry's Concise Commentary

13:31-35 Christ had been glorified in many miracles he wrought, yet he speaks of his being glorified now in his sufferings, as if that were more than all his other glories in his humbled state. Satisfaction was thereby made for the wrong done to God by the sin of man. We cannot now follow our Lord to his heavenly happiness, but if we truly believe in him, we shall follow him hereafter; meanwhile we must wait his time, and do his work. Before Christ left the disciples, he would give them a new commandment. They were to love each other for Christ's sake, and according to his example, seeking what might benefit others, and promoting the cause of the gospel, as one body, animated by one soul. But this commandment still appears new to many professors. Men in general notice any of Christ's words rather than these. By this it appears, that if the followers of Christ do not show love one to another, they give cause to suspect their sincerity.