Today is the Solemnity of the Most Holy Trinity. Here’s an excerpt from the Catechism of the Catholic Church on the Trinity (C.C.C. 234):
"The mystery of the Most Holy Trinity is the central mystery of Christian faith and life. It is the mystery of God in himself. It is therefore the source of all the other mysteries of faith, the light that enlightens them. It is the most fundamental and essential teaching in the "hierarchy of the truths of faith." The whole history of salvation is identical with the history of the way and the means by which the one true God, Father, Son, and Holy Spirit, reveals himself to men "and reconciles and unites with himself those who turn away from sin."
Let us pray,
Most Holy Trinity, Father, Son and Holy Spirit, I adore Thee profoundly. I offer Thee the most precious Body, Blood, Soul and Divinity of Jesus Christ, present in all the tabernacles of the world, in reparation for the outrages, sacrileges and indifferences whereby He is offended. And through the infinite merits of His Most Sacred Heart and the Immaculate Heart of Mary, I beg of Thee the conversion of poor sinners. Amen.