Salvation is purely a function of God's grace, of which there is no set formula. He will dispense that grace to whomever He wants, and for whatever reasons He wants. There are, however, formulas for standard professions of faith, and it's those professions that define what orthodox Christian belief is (with the assumption that being of orthodox belief is the surest known way of being in accordance with said grace and eventual salvation).
These professions were usually made for the specific purpose of refuting one or multiple heresies, of which there were many in the Early Church period. It's not that heresies haven't persisted, or resurfaced, or new ones haven't formed, but the course of history allowed the Pauline tradition to solidify and coalesce into what we know today as being orthodox, and regardless of whether one is Catholic, Orthodox, Anglican, or of one of the various schools of thought within Protestantism, the one thing (or well, group of things) they have in common is that they are all Pauline (Restorationists, despite being an offshoot of 19th century Protestantism, may or may not be Pauline - some are and some aren't). The overall standard profession of course being the Nicene creed:
Code:
We believe in one God,
the Father, the Almighty,
maker of heaven and earth,
of all that is, seen and unseen.
We believe in one Lord, Jesus Christ,
the only Son of God,
eternally begotten of the Father,
God from God, Light from Light,
true God from true God,
begotten, not made,
of one Being with the Father;
through him all things were made.
For us and for our salvation
he came down from heaven,
was incarnate of the Holy Spirit and the Virgin Mary
and became truly human.
For our sake he was crucified under Pontius Pilate;
he suffered death and was buried.
On the third day he rose again
in accordance with the Scriptures;
he ascended into heaven
and is seated at the right hand of the Father.
He will come again in glory to judge the living and the dead,
and his kingdom will have no end.
We believe in the Holy Spirit, the Lord, the giver of life,
who proceeds from the Father [and the Son*],
who with the Father and the Son is worshiped and glorified,
who has spoken through the prophets.
We believe in one holy catholic and apostolic Church.
We acknowledge one baptism for the forgiveness of sins.
We look for the resurrection of the dead,
and the life of the world to come. Amen
*the infamous filoque clause.
The Chalcedonian and Athanasian creeds are even more direct about the nature of Christ and the underlying belief of what Trinitarianism consists of, but these don't necessarily see as wide usage as the Nicene (or even the Apostles') creed, especially in Protestant churches.