The account of Jesus’ baptism in Mark 1 clearly states that 1) Jesus went into the water, 2) the Spirit descended on Him, and 3) God’s voice was heard from heaven. So where did this idea of a holy trinity come from? The very first indication of the idea of a “trinity” came from Iraneus. Why was his word valued so much? Well, he had learned from Polycarp who was a disciple of the apostle John. So Iraneus had a connection to one of Christ’s apostles that gave his words extra weight. (Source) The idea of the trinity seems to have started with good intentions– there was a desire to combat false ideas about multiple gods. But over the years with the growth of Christianity, there was a need to establish specific rules and guidelines to govern such a large church. Constantine who ruled Rome recognized that if there was division in the Christian church it could create division in his empire, and so he called the Council of Nicea (modern-day Turkey) where the idea of the trinity became firmly established. (Source) This belief was that God, Jesus, and the Holy Spirit were one god of the same substance– basically one being. It’s like one actor in a movie playing three roles. (Source)