The mystery of the Holy Trinity is the central mystery of the Christian faith and life. God reveals himself as Father, Son, and Holy Spirit. The doctrine of the Trinity includes three truths of faith.
First, the Trinity is One. We do not speak of three gods but of one God. Each of the Persons is fully God. They are a unity of Persons in one divine nature.
Second, the Divine Persons are distinct from each other. Father, Son, and Spirit are not three appearances or modes of God, but three identifiable persons, each fully God in a way distinct from the others.
Third, the Divine Persons are in relation to each other. The distinction of each is understood only in reference to the others. The Father cannot be the Father without the Son, nor can the Son be the Son without the Father. The Holy Spirit is related to the Father and the Son who both send him forth.
All Christians are baptized in the name of the Father and of the Son and of the Holy Spirit. The Trinity illumines all the other mysteries of faith.
This article is an excerpt from the United States Catholic Catechism for Adults, copyright © 2006, United States Conference of Catholic Bishops. All rights reserved. Used with permission.