(Athanasian Symbol - Prime, Office of the Feast of the Most Holy Trinity)
Which faith except every one do keep whole and undefiled, * without doubt he shall perish eternally.
Now the Catholic faith is this, * that we worship one God in Trinity, and Trinity in Unity.
Neither confounding the Persons, * nor dividing the substance.
For there is one Person of the Father, another of the Son, * and another of the Holy Ghost.
But the Godhead of the Father, of the Son, and of the Holy Ghost is one, * the Glory Equal, the Majesty Co-Eternal.
Such as the Father is, such is the Son, * and such is the Holy Ghost.
The Father Uncreated, the Son Uncreated, * and the Holy Ghost Uncreated.
The Father Infinite, the Son Infinite, * and the Holy Ghost Infinite.
The Father Eternal, the Son Eternal, * and the Holy Ghost Eternal.
And yet they are not three Eternals, * but one Eternal.
As also they are not three Uncreated, nor three Infinites, * but One Uncreated, and One Infinite.
So likewise the Father is Almighty, the Son Almighty, * and the Holy Ghost Almighty.
And yet they are not three Almighties, * but One Almighty.
So the Father is God, the Son God, * and the Holy Ghost God.
And yet they are not three Gods, * but One God.
So the Father is Lord, the Son Lord, * and the Holy Ghost Lord.
And yet they are not three Lords, * but One Lord.
For, like as we are compelled by Christian truth to acknowledge every Person by Himself to be God and Lord, *
so are we forbidden by the Catholic Religion to say, there be three Gods or three Lords.
The Father is made of none, * neither created, nor begotten.
The Son is of the Father alone: * not made, nor created, but begotten.
The Holy Ghost is of the Father, and the Son: * not made, nor created, nor begotten, but proceeding.
So there is One Father, not three Fathers; one Son, not three Sons; * one Holy Ghost, not three Holy Ghosts.
And in this Trinity is nothing afore or after, nothing is greater or less; *
but the whole three Persons are Co-Eternal together, and Co-Equal.
So that in all things, as is aforesaid, * the Unity in Trinity, and the Trinity in Unity is to be worshipped.
He therefore that willeth to be safe, * let him thus think of the Trinity.
But it is necessary to eternal salvation, * that he also believe faithfully the Incarnation of our Lord Jesus Christ.
The right Faith therefore is, that we believe and confess, * that our Lord Jesus Christ, the Son of God, is God and man.
God, of the Substance of the Father, Begotten before the worlds: *
and Man, of the substance of His mother, born in the world.
Perfect God, Perfect Man, * of a reasoning soul and human flesh subsisting.
Equal to the Father as touching His Godhead, * inferior to the Father as touching His Manhood.
Who, although He be God and Man, * yet He is not two, but One Christ.
One, however, not by conversion of the Godhead into Flesh, * but by taking of the Manhood into God.
One altogether, not by confusion of Substance, * but by Unity of Person.
For as the reasoning soul and flesh is one man, * so God and man is One Christ.
Who suffered for our salvation, descended into hell, * rose again the third day from the dead.
He ascended into heaven, He sitteth on the right hand of the Father, God Almighty, *
from whence He shall come to judge the quick and the dead.
At whose coming all men shall rise again with their bodies, * and shall give account for their own works.
And they that have done good shall go into life eternal, * but they that have done evil into eternal fire.
This is the Catholic Faith, * which except a man believe faithfully and firmly, he cannot be safe.
V. Glory be to the Father, and to the Son, * and to the Holy Ghost.
R. As it was in the beginning, is now, * and ever shall be, world without end. Amen.
Ps. 109 (Dixit Dominus - RV 594): Dox.