God revealed Himself to us in 3 forms, but He is still one God.
Trinity appears no where in Scripture. Trinity speaks of 3 separate Gods. Triune speaks of 3 forms of one God. If God was a Trinity, I suppose it makes it easier to worship Mary, John, Paul, Peter, and other saints. There is but one God and all our worship should be His.
How could Melchizedek, have no beginning and no end, be a High Priest forever, be the King of Salem, and have no genealogy? God appeared on earth in bodily form thousands of years before the birth of Christ. To a Jew, a King and a Priest cannot be the same person, unless He is in the order Melchizedek. Melchizedek was a theophany of Jesus or Jesus is not a High Priest forever. If He had no beginning or end, one could say Jesus was born of Mary and died on the cross so we should be looking to Melchizedek for salvation.
God is Spirit and can appear in whatever form He chooses. Was the burning bush God? No, God was in the form of a burning bush. Jesus is the fleshly form God took to be a final sacrifice for His people, but there is still but one God. If God is spirit, is the Holy Spirit God, or a part of God, or another God?