John 13

In His final hours, the Savior taught His disciples -

"A new commandment I give unto you, That ye love one another; as I have loved you, that ye also love one another." (New Testament | John 13:34)

It is obvious that this is not the first time that the children of Abraham had been commanded to love one another. Elder Bruce R. McConkie provided this explanation -

"Yes, and an old commandment too; a commandment both old and new, a commandment that commences now and yet is everlasting; a commandment that is new each time it is revealed, but is old because it has always been in force. John, who here preserves this saying of our Savior, amplified and explained it in his own writings. Speaking of the "love of God," he said: "Brethren, I write no new commandment unto you, but an old commandment, which ye had from the beginning." And then speaking also of the same thing he says: "Again, a new commandment I write unto you." (1 John 2:1-8.)

This gospel manner of naming the same thing as being both new and old is nowhere better illustrated than in the designation, "the new and everlasting covenant." The gospel is the everlasting covenant, the covenant of salvation which God always has and always will make with men, but it is a new covenant each time it is revealed. The gospel we have today is new to the world for this era; it is old because it was had anciently; it is everlasting because it is the same from age to age and from eternity to eternity." (DNTC 1:726.)

But with this new commandment, in a sense, a litmus test is given -

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

It becomes clear that we are only disciples of Jesus Christ if we love and have compassion for each other.