The Apostle John urges us: "Beloved, let us love one another; for love is of God, and he who loves is born of God and knows God. He who does not love does not know God; for God is love" (1 Jn 4: 7-8).
While these sublime words reveal to us the very essence of God as a mystery of infinite charity, they also lay the basis for the Christian moral life, which is summed up in the commandment of love.
The human person is called to love God with total commitment and to relate to his brothers and sisters with a loving attitude inspired by God's own love. Conversion means being converted to love.
In the Old Testament the inner dynamics of this commandment can already be seen in the covenant relationship established by God with Israel: on the one hand, there is the initiative of God's love, and, on the other, the response of love that he expects from Israel. This is how, for example, the divine initiative is presented in the Book of Deuteronomy: "It was not because you were more in number than any other people that the Lord set his love upon you and chose you, for you were the fewest of all peoples; but it is because the Lord loves you" (Dt 7: 7-8). The basic commandment that directs Israel's entire religious life corresponds to this preferential, totally gratuitous love: "You shall love the Lord your God with all your heart, and with all your soul, and with all your might" (ibid., 6: 5).
The loving God is a God who is not remote, but intervenes in history. When he reveals his name to Moses, he does so to assure him of his loving assistance in the saving event of the Exodus, an assistance which will last for ever (cf. Ex 3: 15). Through the prophets' words, he would continually remind his people of this act of love. We read, for example, in Jeremiah: "Thus says the Lord: "The people who survived the sword found grace in the wilderness; when Israel sought for rest, the Lord appeared to him from afar. I have loved you with an everlasting love; therefore I have continued my faithfulness to you'" (Jer 31: 2-3).
It is a love which takes on tones of immense tenderness (cf. Hos 11: 8f.; Jer 31: 20) and normally uses the image of a father, but sometimes is also expressed in a spousal metaphor: "I will betroth you to me for ever; I will betroth you to me in righteousness and in justice, in steadfast love and in mercy" (Hos 2: 19; cf. vv. 18-25).
Even after seeing his people's repeated unfaithfulness to the covenant, this God is still willing to offer his love, creating in man a new heart that enables him to accept the law he is given without reserve, as we read in the prophet Jeremiah: "I will put my law within them, and I will write it upon their hearts" (Jer 31: 33). Likewise in Ezekiel we read: "A new heart I will give you, and a new spirit I will put within you; and I will take out of your flesh the heart of stone and give you a heart of flesh" (Ez 36: 26).
In the New Testament this dynamic of love is centred on Jesus, the Father's beloved Son (cf. Jn 3: 35; 5: 20; 10: 17), who reveals himself through him. Men and women share in this love by knowing the Son, that is, by accepting his teaching and his work of redemption.
We can only come to the Father's love by imitating the Son in his keeping of the Father's commandments: "As the Father has loved me, so have I loved you; abide in my love. If you keep my commandments, you will abide in my love, just as I have kept my Father's commandments and abide in his love" (ibid., 15: 9-10). In this way we also come to share in the Son's knowledge of the Father: "No longer do I call you servants, for the servant does not know what his master is doing; but I have called you friends, for all that I have heard from my Father I have made known to you" (ibid., v. 15).
Love enables us to enter fully into the filial life of Jesus, making us sons in the Son: "See what love the Father has given us, that we should be called children of God; and so we are. The reason why the world does not know us is that it did not know him" (1 Jn 3: 1). Love transforms life and enlightens our knowledge of God to the point that it reaches that perfect knowledge of which St Paul speaks: "Now I know in part; then I shall understand fully, even as I have been fully understood" (1 Cor 13: 12).
It is necessary to stress the relationship between knowledge and love. The inner conversion which Christianity offers is a genuine experience of God, in the sense indicated by Jesus in his priestly prayer at the Last Supper: "This is eternal life, that they know you the only true God, and Jesus Christ whom you have sent" (Jn 17: 3). Knowledge of God, of course, also has an intellectual dimension (cf. Rom 1: 19-20), but the living experience of the Father and the Son occurs through love, that is, in the last analysis, in the Holy Spirit, because "God's love has been poured into our hearts through the Holy Spirit" (Rom 5: 5).
The Paraclete is the One through whom we experience God's fatherly love. Moreover, the most comforting effect of his presence in us is precisely the certainty that this eternal and boundless love with which God loved us first will never abandon us: "Who shall separate us from the love of Christ? ... For I am sure that neither death, nor life, nor angels, nor principalities, nor things present, nor things to come, nor powers, nor height, nor depth, nor anything else in all creation, will be able to separate us from the love of God in Christ Jesus our Lord" (ibid., 8: 35, 38-39). The new heart, which loves and knows, beats in harmony with God who loves with an everlasting love.