From Pope St. John Paul II’s encyclical Veritatis Splendor (1993):
Jesus asks us to follow him and to imitate him along the path of love, a love which gives itself completely to the brethren out of love for God: “This is my commandment, that you love one another as I have loved you” (Jn 15:12). The word “as” requires imitation of Jesus and of his love, of which the washing of feet is a sign: “If I then, your Lord and Teacher, have washed your feet, you also ought to wash one another’s feet. For I have given you an example, that you should do as I have done to you” (Jn 13:14-15). Jesus’ way of acting and his words, his deeds and his precepts constitute the moral rule of Christian life. Indeed, his actions, and in particular his Passion and Death on the Cross, are the living revelation of his love for the Father and for others. This is exactly the love that Jesus wishes to be imitated by all who follow him. It is the “new” commandment: “A new commandment I give to you, that you love one another; even as I have loved you, that you also love one another. By this all men will know that you are my disciples, if you have love for one another” (Jn 13:34-35).
The word “as” also indicates the degree of Jesus’ love, and of the love with which his disciples are called to love one another. After saying: “This is my commandment, that you love one another as I have loved you” (Jn 15:12), Jesus continues with words which indicate the sacrificial gift of his life on the Cross, as the witness to a love “to the end” (Jn 13:1): “Greater love has no man than this, that a man lay down his life for his friends” (Jn 15:13).
As he calls the young man to follow him along the way of perfection, Jesus asks him to be perfect in the command of love, in “his” commandment: to become part of the unfolding of his complete giving, to imitate and rekindle the very love of the “Good” Teacher, the one who loved “to the end”. This is what Jesus asks of everyone who wishes to follow him: “If any man would come after me, let him deny himself and take up his cross and follow me” (Mt 16:24).
— Veritatis Splendor 20