To love one another is an old commandment, as old as the human race. But "as I have loved you" is new. The manner by which we love, the process by which this can occur is new.
The old commandment was there from the beginning. We are our brother's keeper. No man is an island. We have a responsibility to love each other. But we have never found the way until we find it in the sharing of the life of Jesus, the fellowship with the Son of God. In the light of that new power it is now possible to perform the old commandment.