This is my commandment. Since it is proper that we regulate our life according to the commandment of Christ, it is necessary, first of all, that we should understand what it is that he wills or commands He now therefore repeats what he had formerly said, that it is his will, above all things, that believers should cherish mutual love among themselves. True, the love and reverence for God comes first in order, but as the true proof of it is love toward our neighbors, he dwells chiefly on this point. Besides, as he formerly held himself out for a pattern in maintaining the general doctrine, so he now holds himself out for a pattern in a particular instance; for he loved all his people, that they may love each other. Of the reason why he lays down no express rule, in this passage, about loving unbelievers, we have spoken under the former chapter.

This is my commandment - The special law of Christianity, called hence "the new commandment." See the notes at John 13:34.
As I have loved you - That is, with the same tender affection, willing to endure trials, to practice self-denials, and, if need be, to lay down your lives for each other, 1-John 3:16.

That ye love one another - See on John 13:34 (note). So deeply was thus commandment engraved on the heart of this evangelist that St. Jerome says, lib. iii. c. 6, Com. ad Galat., that in his extreme old age, when he used to be carried to the public assemblies of the believers, his constant saying was, Little children, love one another. His disciples, wearied at last with the constant repetition of the same words, asked him, Why he constantly said the same thing? "Because (said he) it is the commandment of the Lord, and the observation of it alone is sufficient." Quia praeceptum Domini est, et, si solum fiat, sufficit.

This is my commandment, that ye love one another,.... Christ had been before speaking of his commandments; and he mentions this as the principal one, and to which all the rest may be reduced; for as the precepts of the second table of the moral law may be briefly comprehended in this one duty, love to our neighbour, so all the duties of Christianity, relative to one another, are reducible to this, by love to serve each other. This was the commandment which lay uppermost on Christ's heart, and which he knew, if attended to, the rest could not fail of being observed. The argument by which, and the manner in which, he presses it, is as before:
as I have loved you; than which nothing can be more strong and forcible; see John 13:34.

That ye love one another, &c.--(See on John 13:34-35).

Your joy will be full, if ye so love one another.