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.
Taken from The Basic Catholic Catechism
PART TWO: The Apostle's Creed
First Article of the Creed: "I believe in God the Father Almighty, Creator of heaven and earth."
By William G. Most. (c)Copyright 1990 by William G. Most
Related Q and A
25. How many Persons are there in God?
In God there are three divine Persons--the Father, the Son, and the Holy Ghost.
(a) Unaided by divine revelation, the human mind could not know the existence of the Blessed Trinity because it is a supernatural mystery.3 Even after God has revealed the existence of the Blessed Trinity, we cannot understand it fully. When we believe, on the word of God, that there are three Persons in one God, we do not believe that three Persons are one Person, or that three gods are one God; this would be a contradiction.
26. Is the Father God?
The Father is God and the first Person of the Blessed Trinity.
(a) The first Person of the Blessed Trinity is called the Father because from all eternity He begets the second Person, His only-begotten Son.
(b) God the Father is called the first Person not because He is greater or older than the other two Persons, but because He is unbegotten.
27. Is the Son God?
The Son is God and the second Person of the Blessed Trinity.
(a) The second Person of the Blessed Trinity is called the Son because from all eternity, He is the only begotten of the Father. Proceeding from the Father, the Son is called the Divine Word or the Wisdom of the Father.
28. Is the Holy Ghost God?
The Holy Ghost is God and the third Person of the Blessed Trinity.
(a) The third Person of the Blessed Trinity is called the Holy Ghost because from all eternity He is breathed forth, as it were, by the Father and the Son. Proceeding from the Father and the Son, He is called the Gift or Love of the Father and the Son.
(b) The word "Ghost" applied to the third Person means "Spirit."
29. What do we mean by the Blessed Trinity?
By the Blessed Trinity we mean one and the same God in three divine Persons.
30. Are the three divine Persons really distinct from one another?
The three divine Persons are really distinct from one another.
(a) Although the Father, the Son, and the Holy Ghost are distinct Persons, they are not distinct in nature. The nature of the Father is entirely the nature of the Son; and the nature of the Father and the Son is entirely the nature of the Holy Ghost.
31. Are the three divine Persons perfectly equal to one another?
The three divine Persons are perfectly equal to one another, because all are one and the same God.
(a) No one of the three Persons precedes the others in time or in power, but all are equally eternal and all-powerful because they have the same divine nature.
32. How are the three divine Persons, though really distinct from one another, one and the same God?
The three divine Persons, though really distinct from one another, are one and the same God because all have one and the same divine nature.
(a) Because the three divine Persons have one and the same divine nature, they have the same perfections and the same external works are produced by them. But in order that we may better know the three divine Persons, certain perfections and works are attributed to each Person; for example, omnipotence and the works of omnipotence, such as creation, to the Father; wisdom and the works of wisdom, such as enlightenment, to the Son, love and the works of love, such as sanctification, to the Holy Ghost.
33. Can we fully understand how the three divine Persons, though really distinct from one another, are one and the same God?
We cannot fully understand how the three divine Persons, though really distinct from one another, are one and the same God because this is a supernatural mystery.
34. What is a supernatural mystery?
A supernatural mystery is a truth which we cannot fully understand, but which we firmly believe because we have God's word for it.
(a) In addition to those truths which can be attained by man's natural reason, there are certain mysteries hidden in God which we cannot know without divine revelation, but which we must believe because God has revealed them. Divine mysteries by their very nature are far above the power of human understanding and even when revealed and accepted on faith they remain obscure during our life on earth. To understand these things fully, a finite mind would have to comprehend the infinite.
(b) In heaven there will be a fuller understanding of these mysteries, but never an infinite comprehension of them.
It is reasonable to believe supernatural mysteries revealed by God because He can neither deceive nor be deceived. In our everyday life we believe many things on the word of human beings even though at times they deceive or are deceived.
The Baltimore Catechism, no. 3, Lesson 3.