Most contemporary Christians are polytheists. They believe in many gods-unawares, of course. There is a Father-god, depicted old and white-haired; there is a Son-god, middle-aged, identified with Jesus of Nazareth; and there is a Spirit-god, symbolized by a dove. Many artists have depicted this trinity, like El Greco, who painted his "The Trinity" in 1578. These three gods are believed to constitute only one divinity, but very few ordinary Christians could explain how this could be the case. This plurality of gods is the reason why Christianity is reviled by Jews and Muslims who affirm steadfastly the unicity of God and who ban any pictorial representation of the divinity.
The very first Christians, the family and friends of Jesus, who were Jews, would not have held such a pagan belief, but their writings were destroyed by later adherents, so we lack the evidence to prove this.
Christians claim that the Trinity has been revealed, but the fact is that such revelation is disproved by science and philosophy. So why not transcend this trinity in a contemplation of the One Unknowable God of all? Why not learn to live without knowing what God is, being satisfied with the belief that God is neither male nor female, neither triad nor monad, but simply the Divine Incognito?