Jesus knew that his disciples would not fully understand him, since the Spirit had not been poured out. They were blind without the ability to trust, nor had they impulse to love, "for God is love, and he who abides in love abides in God and God in him". The Holy Trinity is love. Since love between the Persons of the Holy Trinity engenders unity that endures, Jesus wished the principle moving the Holy Trinity to be incarnate in mankind, and that the source of holiness become actual in his disciples.
So Jesus exhorted his disciples for mutual love among the members of his Church. He did not lay down ten prohibitions as was the case in the Old Testament, but only one commandment covering all other divine commandments. Love is the fulfillment of Law. Whereas Moses gave people negative rules, Christ impels us to positive action, as he exemplified himself. Love is the essence in Church life. Where the Church shows no love, it ceases to be the Church.
Love is the secret of Christ’s person. He had compassion on the sheep that went astray as a shepherd would, and had mercy on the lost sheep. He bore with his disciples patiently and gently. Christ made love the charter of his Kingdom. He who loves abides in Jesus’ graciousness, but he who hates belongs to Satan. Love is kind and does not become puffed up. It is patient, hoping all that is good even to the foe, just as our apostles laid down its traits in Epistles several times. God’s love never fails; it is the bond of perfection.
For the Church there is no other sign save sacrifice for love’s sake. If we train ourselves for service we become his disciples. We learn as guided by Jesus the meaning of practical love. We live in his pardon, and forgive others gladly. If no one in an assembly strives for greatness, and if all rejoice because the Spirit of Christ has united them, there heaven comes to earth, and our living Lord establishes churches filled with the Holy Spirit.