The early Christians had a very dramatic change in their thinking and beliefs where Jesus became known as God, as did when the Holy Spirit became known as the third member of the Trinity.
Think of this , Jewish were strictly Monotheistic. There is only One God. So when the early Christians, the Apostles and Disciples were attempting to understand who Jesus was, and what His death and Resurrection were about, they were worshipping Him very early after the Resurrection as God. We read this in the Pauline letters. But the Pauline letters were written about 20 years after the death of Jesus.
So to incorporate Jesus into the concept of God, and the Son of God, they did not become polytheistic. They were guided to know Jesus was the same, the one God. And later the Holy Spirit.
It was the experience of the Resurrection that started early Christianity, The interactions and actions of Jesus as physically present in the 40 days He appeared and interacted with people.
Stephen was the first to profess publicly, in the New Testament, what the early christians were living and knowing and teaching. Stephan was killed for it. For being a Christian and professing Jesus, the human Jesus that had walked the earth with many living , was God.
Stephen’s testimony tells us, the very early Christians in the time after Jesus Death, knew He was the Son of God, and God. And knew the outpouring of the Holy Spirit was also God.