Solemnity of the Holy Trinity: The Athanasian Creed

On the Feast of the Most Holy Trinity, in the Divine Office of Prime, the Athanasian Creed is said.  And it leaves no doubt as to the unity of the Holy Trinity!  It has been used by Christian churches since the sixth century, and is the first creed in which the equality of the three persons of the Trinity is explicitly stated. There’s an interesting article at Wikipedia.

Pay close attention to the last statement of this Creed: "This is the Catholic Faith, * which except a man believe faithfully and firmly, he cannot be saved."

Canticum Quicumque (Athanasian Creed)

Whosoever willeth to be saved, * before all things it is necessary that he hold the Catholic faith.

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 saved.
 

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.

Ant. Glory be to thee, O equal Trinity * one Deity, from before all ages, so now and for evermore.