The Holy Trinity
Perhaps the deepest, the most profound of all mysteries is the mystery of the Trinity. The Church teaches us that although there is only one God, yet, somehow, there are three Persons in God. The Father is God, the Son is God, the Holy Spirit is God, yet we do not speak of three Gods, but only one God. They have the same nature, substance, and being.
We came to know this immense mystery because Christ revealed it to us. Just before ascending He told them: "Go teach all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit" (Matthew 28:19). We know that these Three are not just different ways of looking at one person. For at the Last Supper, Jesus told us: "I came forth from the Father." So He is different from the Father. But He also promised: "If I go, I will send Him [the Paraclete] to you. . . . He will guide you to all truth" (John 16:28, 7, 13). So the Holy Spirit is also different.
Even though the Three Persons are One God, yet they are distinct: for the Father has no origin, He came from no one. But the Son is begotten, He comes from the Father alone. The Holy Spirit comes or proceeds from both the Father and the Son. These different relations of origin tell us there are three distinct Persons, who have one and the same divine nature.
Even though everything the Three Persons do outside the Divine nature is done by all Three, yet it is suitable that we attribute some works specially to one or the other Person. So we speak of the Father especially as the power of creation, of the Son as the wisdom of the Father, of the Holy Spirit as goodness and sanctification.
The two doctrines of the Trinity and the Incarnation are the foundation of Christian life and worship. By becoming man, God the Son offered us a share in the inner life of the Trinity. By grace, we are brought into the perfect communion of life and love which is God, Father, Son and Holy Spirit. This sharing in the life of the Trinity is meant to culminate in heaven, where we will see the three Persons face to face, united to them in unspeakable love.
(by Rev. William G. Most at www,ewtn.com)