Oremus

Whoever wishes to be saved must, above all, keep the Catholic faith. For unless a person keeps this faith whole and entire he will undoubtedly be lost forever. This is what the Catholic faith teaches: we worship one God in the Trinity and the Trinity in unity. We distinguish among the persons, but we do not divide the substance. For the Father is a distinct person; the Son is a distinct person; and the Holy Spirit is a distinct person.
Still the Father and the Son and the Holy Spirit have one divinity, equal glory, and coeternal majesty. What the Father is, the Son is, and the Holy Spirit is. The Father is uncreated, the Son is uncreated, and the Holy Spirit is uncreated. The Father is boundless, the Son is boundless, and the Holy Spirit is boundless. The Father is eternal, the Son is eternal, and the Holy Spirit is eternal.
Nevertheless, there are not three eternal beings, but one eternal being. Thus there are not three uncreated beings, nor three boundless beings, but one uncreated being and one boundless being. Likewise, the Father is omnipotent, the Son is omnipotent, and the Holy Spirit is omnipotent. Yet there are not three omnipotent beings, but one omnipotent being. Thus the Father is God, the Son is God, and the Holy Spirit is God. But there are not three gods, but one God. The Father is Lord, the Son is Lord, and the Holy Spirit is Lord. There as not three lords, but one Lord. For according to Christian truth, we must profess that each of the persons individually is God; and according to Christian religion we are forbidden to say that there are three gods or lords. The Father is not made by anyone, nor created by anyone, nor generated by anyone. The Son is not made nor created, but he is generated by the Father alone. The Holy Spirit is not made nor created nor generated, but proceeds from the Father and the Son.
There is, then, one Father, not three Fathers; one Son, but not three sons; one Holy Spirit, not three holy spirits. In this Trinity, there is nothing greater, nothing less than anything else. But the entire three persons are coeternal and coequal with one another. So that, as we have said, we worship complete unity in the Trinity and the Trinity in unity.
This, then, is what he who wishes to be saved must believe about the Trinity. It is also necessary for eternal salvation that he believes steadfastly in the incarnation of our Lord Jesus Christ. The true faith is: we believe and profess that our Lord Jesus Christ, the Son of God, is both God and man. As God He was begotten of the substance of the Father before time; as man He was born in time of the substance of His Mother. He is perfect God; and He is perfect man, with a rational soul and human flesh. He is equal to the Father in His divinity, but He is inferior to the Father in His humanity. Although He is God and man, He is not two, but one Christ. And He is one, not because His divinity was changed into flesh, but because His humanity was assumed to God. He is one, not at all because of a mingling of substances, but because He is one person. As a rational soul and flesh are one man: so God and man are one Christ.
He died for our salvation, descended to hell, arose from the dead on the third day. Ascended into heaven, sits at the right hand of God the Father almighty, and from there He shall come to judge the living and the dead. At His coming, all men are to arise with their own bodies; and they are to give an account of their lives. Those who have done good deeds will go into eternal life; those who have done evil will go into everlasting fire.
This is the Catholic faith. Everyone must believe it, firmly and steadfastly; otherwise He cannot be saved. Amen.