Albert Barnes Commentary John 13:35

"By this shall all men know that ye are my disciples, if ye have love one to another." — John 13:35 (ASV)

By this shall all men, etc. That is, your love for each other will be so decisive evidence that you are like the Saviour, that all men will see and know it. It will be the thing by which you will be known among all men. You will not be known by peculiar rites or habits; not by a peculiar form of dress or manner of speech; not by peculiar austerities and unusual customs, like the Pharisees, the Essenes, or the scribes, but by deep, genuine, and tender affection.

And it is well known that this was what eminently distinguished the first Christians and was the subject of remark by the surrounding pagans. "See," said the heathen, "see how they love one another! They are ready to lay down their lives for each other." Alas! how changed is the spirit of the Christian world since then!

Perhaps, of all the commands of Jesus, the observance of this is what is least apparent to a surrounding world. It is not so much that they are divided into different sects, for this may be consistent with love for each other; but it is the lack of deep-felt, genuine love toward Christians even of our own denomination; the absence of genuine self-denial; the pride of rank and wealth; and the fact that professed Christians are often known by anything else rather than by true attachment to those who bear the same Christian name and image.

The true Christian loves religion wherever it is found—equally in a prince or in a slave, in the mansion of wealth or in the cottage of poverty, on the throne or in the hut of want. He overlooks the distinction of sect, of colour, and of nations; and wherever he finds a person who bears the Christian name and manifests the Christian spirit, he loves him. And this, more and more as the millennium draws near, will be the distinctive badge of the professed children of God. Christians will love their own denominations less than they love the spirit and temper of the Christian, wherever it may be found.