Jesus was a descendant of David and of Abraham (Matt. 1:1). Born in Israel, he was raised by Jewish parents in a Jewish community. He grew up attending the synagogue, learning the Scriptures and the words of the prophets. His earliest followers were people who from their youth were wholly dedicated to YHWH alone as God.
It is Jesus the Jew and his Jewish disciples who were the original teachers of Christianity. They were the true fathers of the Christian church. There was a wonderful continuity between the Jewish founders of Christianity and God’s prophets of old. They all believed that only one individual is God: The Father of Jesus Christ. The first Christians were solidly grounded in YHWH alone as the God of Israel and in Jesus as his Messiah, his greatest anointed king. Jesus himself summarized these very things at the beginning of his great intercessory prayer which is recorded in the Gospel of John:
Father … this is eternal life: that they may know you, the only true God, and Jesus Christ whom you have sent ( John 17:3).
Jesus did not come to bring the world a different definition of God. He came to affirm the same one that God’s prophets and people of old had been proclaiming from the beginning. Confirming that the Father is the only true God, Jesus then speaks of himself not as God, but as God’s Messiah, the Christ. The God of Israel is the God of Jesus. Original Christianity is the realization of true biblical faith from Abraham to John the Baptist.
Gill, J. Dan (2016). Jesus and Original Christianity. In, The One: In Defense of God (pp. 242-243). Nashville, TN: 21st Century Reformation Publishing.