In making this request to love one another, Jesus is thinking about the role he wants them to perform as his representatives. He is asking them to live as he had lived during the years when he was here, that is, with a life of love. This was to be the distinguishing mark of his disciples. It was not appropriate to speak about this topic as long as Judas was among them.
This request of Jesus is connected to the moral law of God originally revealed in the Old Testament. The summary of appropriate response to God’s law is to love him with all our heart, soul, mind and strength and to love our neighbour as ourselves. Our neighbours fall into two categories: our friends and our enemies. In the Sermon on the Mount, the role model for believers is God’s acts of goodness to his enemies. Here, the role model for loving our friends is the way Jesus has loved his disciples.
It is obvious from the Old Testament that God’s people in that era were expected to love another (Lev. 19:18, 34 ). So how could Jesus describe it as a new commandment? It was new in the sense that, with the coming of the Holy Spirit, they would have a new kind of power to enable them to love as Jesus did.