19 “If you see charity, you see the Trinity”, wrote Saint Augustine. In the foregoing reflections, we have been able to focus our attention on the Pierced one (cf. Jn 19:37, Zech 12:10), recognizing the plan of the Father who, moved by love (cf. Jn 3:16), sent his only-begotten Son into the world to redeem man. By dying on the Cross—as Saint John tells us—Jesus “gave up his Spirit” ( Jn 19:30), anticipating the gift of the Holy Spirit that he would make after his Resurrection (cf. Jn 20:22). This was to fulfil the promise of “rivers of living water” that would flow out of the hearts of believers, through the outpouring of the Spirit (cf. Jn 7:38-39). The Spirit, in fact, is that interior power which harmonizes their hearts with Christ's heart and moves them to love their brethren as Christ loved them, when he bent down to wash the feet of the disciples (cf. Jn 13:1-13) and above all when he gave his life for us (cf. Jn 13:1, 15:13). The Spirit is also the energy which transforms the heart of the ecclesial community, so that it becomes a witness before the world to the love of the Father, who wishes to make humanity a single family in his Son. The entire activity of the Church is an expression of a love that seeks the integral good of man: it seeks his evangelization through Word and Sacrament, an undertaking that is often heroic in the way it is acted out in history; and it seeks to promote man in the various arenas of life and human activity. Love is therefore the service that the Church carries out in order to attend constantly to man's sufferings and his needs, including material needs. And this is the aspect, this service of charity , on which I want to focus in the second part of the Encyclical.
Source: Deus Caritas Est (Vatican.va)