In the ancient world, most people believed in multiple Gods (polytheism), often with geographic jurisdictions. A couple smaller religions (Judaism & Zoroastrianism) taught belief in one God (monotheism). The early church taught belief in One God in Three Persons – Father, Son, and Holy Spirit. Each person of the trinity was co-equal and co-eternal. They did not teach this belief to be socially and philosophically respectable – it was not. They taught it because it was the God who had been revealed to them through the life of Christ. (The heresy of Modalism was rejected because it did not respect the uniqueness of each person of the Trinity. The heresy of tritheism was rejected because it presented the Trinity as 3 gods rather than 1 God.)

Scripture - Matthew 28:16-20, 2 Corinthians 13:14