Feast of the Holy Trinity

The Trinity is the mystery of one God in three Persons: Father, Son, and Holy Spirit. The revealed truth of the Holy Trinity is at the very root of the Church's living faith as expressed in the Creed.
The mystery of the Trinity in itself is inaccessible to the human mind, and is the object of faith only because it was revealed by Jesus Christ, the Divine Son of the Eternal Father.
- Catechism of the Catholic Church

Collect
Father, who sent your Word to bring us truth and your Spirit to make us holy:.Through them we come to know the mystery of your life.Help us to worship you, one God in three Persons, by proclaiming and living our faith in you.We ask you this, Father, Son, and Holy Spirit, one God, true and living, for ever and ever. Amen

Gospel Reading: John 16:12-15
"I have yet many things to say to you, but you cannot bear them now. When the Spirit of truth comes, He will guide you into all the truth; for He will not speak on His own authority, but whatever He hears He will speak, and He will declare to you the things that are to come. He will glorify me, for He will take what is mine and declare it to you. All that the Father has is mine; therefore I said that He will take what is mine and declare it to you.

The Eucharist: at the heart of the Trinity

As the priest mixes a drop of water with the wine, during the preparation of the eucharistic gifts, he says these remarkable words: "By the mystery of this water and wine may we come to share in the divinity of Christ, who humbled himself to share in our humanity".

And there we have it. We are called to share in the divine lief itself. The invitation, issued fully in the person of Jesus, is achieved in him through the power of the Holy Spirit. By our union with Christ, through baptism, through prayer, through the action of the Mass, we are being taken into the heart of the life of the Trinity itself: that exchange of life and love between father, Son and Holy Spirit.

We have no life except with Christ, and with him crucified. In the action of the Mass we are drawn into this one crucial event.

The crucified Christ is the fullness of human prayer. His resurrection is the fullness of God's response. Crucifixion and resurrection: prayer and response. If the crucifixion of the Lord is, as it were, the projection into history of the love of God, then the resurrection of the Lord is the projection into history of the power of the Spirit.

Christ is our salvation.

(extract from The Promise of Future Glory, Reflections on the Mass by Archbishop Vincent Nichols of Birmingham)