The mystery of the Trinity is essentially a mystery of love. The Father delivered his Son as a sacrifice; the Son offered himself to the Father in the Holy Spirit. The Trinity is engaged in the work of salvation and it is Jesus Christ who brings him into our intimate lives so that we can love like God does.
God is perfectly One. He is love in himself. His strength is a force of loving. Baptized in the name of the Father, the Son and the Holy Spirit, we are invited to contemplate the Only God in three persons, to love each of them. St. John in his first epistle (4, 8) said, "God is love." This truth is the most profound in the work of salvation "In this the love of God has been manifested for us: God has sent his only begotten Son into the world that we may live through him" (4, 9 . The Father loves us so much that he sends his Son as Savior of the world. The Father is the model and the principle of love. God wants to dwell in us as the love expressed in our mutual relations. "Since God has loved us, we must love one another" (4:11).
The Trinity remains for us the mystery of the mysteries. It makes us see how God, in the solitude of his being, is total love. God is a community of people so closely linked that they form one being. The Father is the first to be God. By expressing himself, he begets a person who is his own Son, to whom he transmits infinite happiness, infinite power, infinite perfection. He loves his Son so much that this love is detached from him to form a third divine person, the divine person of the Holy Spirit. The Son is the expression, the perfect reply, the word of the Father. He receives everything from the Father and returns to the Father as much as he received in a perfect way. He loves the Father so much that this love is also detached from him to form a third divine person, the divine person of the Holy Spirit. Thus the movement of love is complete because God is a communion of love. This is what we say when we profess our faith: "The Holy Spirit proceeds from the Father and the Son. With the Father and the Son he receives the same adoration and the same glory ... "The Holy Spirit is love in person, gift in person. He is the first one to reach us. He makes the presence of the Father and the Son live in us. Jesus Christ, who introduces us into the Trinitarian mystery, invites us to live in communion according to this model, in the divine community where the three persons form only one love and one being. The Father, the Son and the Holy Spirit continually exult in the Holy Spirit, even in our own hearts. The truth of the Trinity communion of love, is concretely living in all the depth of our person.
The Trinity dwells in Christians and communicates to them His love. In communion our lives are fulfilled. Jesus, the Son of the Father, is sent by him and come to fulfill his will. "Father and I are one. "(John 10:30) All that is to the Son is to the Father and that which is to the Father is to the Son (Jn 17:10); the Father is in the Son and the Son in the Father (John 10:38, Jn 14:10, 17:21). Between the Father and the Son, there is a mutual knowledge (Jn 10, 15, Mt 11, 27, Lk 10, 22), and a mutual love (Jn 3, 35; 5, 20; 14, 31; 15, 9-10; 17, 24).
Jesus Christ who leads us to the Father is present in us by the Holy Spirit. He invites us to enter into the mystery, that is, into the relationship that unites the Son to the Father (Jn 14: 8-9). At the Last Supper, Christ introduced his disciples into the mystery of the Trinity and into the unity. This unity of God can be experienced by Christians in their own lives. It is for them to enter into the perspectives of love of the new covenant, to welcome the coming and the presence of the Holy Spirit in them, to respond to the prayer of Jesus which extends to all the unity of the Trinity, "May all be one. Like you, Father, you are in me and I in you; May they also be one in us. (Jn 17:21) It is in the context of the Last Supper that Christians can enter into the mystery of divine unity.