What Does the
Roman Catholic Church Say?

A Practical Catholic Dictionary, p. 32:

Blessed Trinity, the: One and the same God in three divine persons, the Father, the Son, and the Holy Ghost. There are three distinct persons who are one God. Each of these persons is divine because each one is God. They all have one and the same divine nature. The Father is God and the first person of the Blessed Trinity. The Son is God and the second person of the Blessed Trinity. The Holy Ghost is God and the third person of the Blessed Trinity.”

Catholicism:

“Unless (people) keep this Faith whole and undefiled, without doubt (they) shall perish everlastingly. And the Catholic faith is this: we worship one God in Trinity.”

Handbook for Today’s Catholic, p. 16

“The mystery of the trinity is the central doctrine of Catholic faith. Upon it are based all the other teachings of the church”

The Catholic Encyclopedia

“The term trinity is the term employed to signify the central doctrine of the Christian religion; the truth that in the unity of the Godhead there are three persons.  Thus in the words of the Athanasian Creed, the Father is God, the Son is God and the Holy Spirit is God . . .

“This, the church teaches, is the revelation regarding the nature of God which Jesus Christ, the Son of God, came upon earth to deliver to the world; and which she (the church) proposes to man as the foundation of her whole dogmatic system.”

From the Beginning of the Catholic System

“In the establishment of the Catholic Church, the place of Theodosius is second only to that of Constantine. About the beginning of the year 380 he was baptized by the Catholic bishop of Thessalonica, and immediately afterward he issued the following edict:—

“ . . . Let us believe the sole deity of the Father the Son and the Holy Ghost under an equal majesty and a pious Trinity. We authorize the followers of this doctrine to assume the title of Catholic Christians; and as we judge that all others are extravagant madmen we brand them with the infamous name of ‘heretics, and declare that their conventicles shall no longer usurp the respectable appellation of churches. Besides the condemnation of divine justice they must expect to suffer the severe penalties which our authority guided by heavenly wisdom shall think proper to inflict upon them.

The Encarta Encyclopedia has this to say about the origin of the Trinitarian doctrine:

“Trinity (theology):

In Christian theology, doctrine that God exists as three persons—Father, Son, and Holy Spirit—who are united in one substance or being. The doctrine is not taught explicitly in the New Testament, where the word God almost invariably refers to the Father; but already Jesus Christ, the Son, is seen as standing in a unique relation to the Father, while the Holy Spirit is also emerging as a distinct divine person.

The term trinitas was first used in the 2nd century, by the Latin theologian Tertullian, but the concept was developed in the course of the debates on the nature of Christ (see Christology). In the 4th century, the doctrine was finally formulated; using terminology still employed by Christian theologians, the doctrine taught the coequality of the persons of the Godhead. ... For an adequate understanding of the trinitarian conception of God, the distinctions among the persons of the Trinity must not become so sharp that there seems to be a plurality of gods, nor may these distinctions be swallowed up in an undifferentiated monism.”

 

The Catholic Church has stated:

“Our opponents sometimes claim that no belief should be held dogmatically which is not explicitly stated in Scripture . . . . But the Protestant Churches have themselves accepted such dogmas as the Trinity for which there is no such precise authority in the Gospels.” (Life Magazine, October 30,  1950)

“Q.  Do you observe other necessary truths as taught by the Church, not clearly laid down in Scripture?

“The doctrine of the Trinity, a doctrine the knowledge of which is certainly necessary to salvation, is not explicitly and evidently laid down in Scripture, in the Protestant sense of private interpretation.” (Doctrinal Catechism as quoted in The Review and Herald, August 22, 1854)