I was taught and believed that God is one, that baptism must be done by full immersion and in the name of Jesus only, and that anyone who believed in the Trinity, was baptized by sprinkling or in the name of the Trinity was not a Christian and is going to Hell. I found out later that there were many different beliefs and that hardly anyone agrees with what I was taught. That is why I am studying the beliefs of different churches now and reading the church fathers.
I’ll quote the church father Irenaeus to state what I’m starting to believe at the moment:
“The Church, though dispersed throughout the whole world, even to the ends of the earth, has received from the apostles and their disciples this faith: [She believes] in one God, the Father Almighty, Maker of heaven, and earth, and the sea, and all things that are in them; and in one Christ Jesus, the Son of God, who became incarnate for our salvation; and in the Holy Spirit, who proclaimed through the prophets the dispensations of God, and the advents, and the birth from a virgin, and the passion, and the resurrection from the dead, and the ascension into heaven in the flesh of the beloved Christ Jesus, our Lord, and His [future] manifestation from heaven in the glory of the Father “to gather all things in one,” and to raise up anew all flesh of the whole human race, in order that to Christ Jesus, our Lord, and God, and Savior, and King, according to the will of the invisible Father, “every knee should bow, of things in heaven, and things in earth, and things under the earth, and that every tongue should confess” to Him, and that He should execute just judgment towards all; that He may send “spiritual wickednesses,” and the angels who transgressed and became apostates, together with the ungodly, and unrighteous, and wicked, and profane among men, into everlasting fire; but may, in the exercise of His grace, confer immortality on the righteous, and holy, and those who have kept His commandments, and have persevered in His love, some from the beginning [of their Christian course], and others from [the date of] their repentance, and may surround them with everlasting glory.
As I have already observed, the Church, having received this preaching and this faith, although scattered throughout the whole world, yet, as if occupying but one house, carefully preserves it… For, although the languages of the world are dissimilar, yet the import of the tradition is one and the same. For the Churches which have been planted in Germany do not believe or hand down anything different, nor do those in Spain, nor those in Gaul, nor those in the East, nor those in Egypt, nor those in Libya, nor those which have been established in the central regions of the world. But as the sun, that creature of God, is one and the same throughout the whole world, so also the preaching of the truth shineth everywhere, and enlightens all men that are willing to come to a knowledge of the truth ((Irenaeus, Against Heresies, Book 1, Ch. 10, AD 180)”
So there is one Christian faith taught by the apostles and agreement about a belief in one God, the Lord Jesus, the Holy Spirit, and salvation. The heresies Irenaeus condemned were those that disagreed with the rule of faith. I think Christians disagreed with each other on many other issues but were still considered Christian as long as they agreed on the basic, essential teaching of Jesus and the apostles.