107 And so we can easily understand that the devotion to the Sacred Heart of Jesus, of its very nature, is a worship of the love with which God, through Jesus, loved us, and at the same time, an exercise of our own love by which we are related to God and to other men. Or to express it in another way, devotion of this kind is directed towards the love of God for us in order to adore it, give thanks for it, and live so as to imitate it; it has this in view, as the end to be attained, that we bring that love by which we are bound to God to the rest of men to perfect fulfillment by carrying out daily more eagerly the new commandment which the divine Master gave to His Apostles as a sacred legacy when He said: "A new commandment I give to you, that you love one another as I have loved you. . .This is My commandment that you love one another as I have loved you."(108) And this commandment is really new and Christ's own, for as Aquinas says, "It is, in brief, the difference between the New and the Old Testament, for as Jeremias says, 'I will make a new covenant with the house of Israel.'(109) But that commandment which in the Old Testament was based on fear and reverential love was referring to the New Testament; hence, this commandment was in the old Law not really belonging to it, but as a preparation for the new Law."(110)
Source: Haurietis Aquas (Vatican.va)