The Trinity doctrine claims that the Father, Son and Holy Spirit are three co-equal, co-eternal gods that are not three gods but one god. But how can Jesus be the literal Son of God if He has always existed alongside the Father? And how can the Father be a Father if Jesus is not really His Son? Hence the Trinity doctrine and other similar beliefs like Unitarians deny that Jesus is the literal Son of God in one way or another.
If you do not confess Jesus is the Son of God then you are separated from God. And if you do not believe Jesus is the Son of God and that God gave His literal Son then you make God a liar and you do not have eternal life.