Why was the church so concerned about the doctrine of the Trinity? Is it really essential to hold to the full deity of the Son and the Holy Spirit? Yes it is, for this teaching has implications for the very heart of the Christian faith. First, the atonement is at stake. If Jesus is merely a created being and not fully God, then it is hard to see how he, a creature, could bear the full wrath of God against all of our sins. Could any creature, no matter how great, really save us? Second, justification by faith alone is threatened if we deny the full deity of the Son. (This is seen today in the teaching of the Jehovah’s Witnesses, who do not believe in justification by faith alone.) If Jesus is not fully God, we would rightly doubt whether we can really trust him to save us completely. Could we really depend fully on any creature for our salvation? Third, if Jesus is not infinite God, should we pray to him or worship him? Who but an infinite, omniscient God could hear and respond to all the prayers of all God’s people? And who but God himself is worthy of worship? Indeed, if Jesus is merely a creature, no matter how great, it would be idolatry to worship him—yet the New Testament commands us to do so (Phil. 2:9–11; Rev. 5:12–14). Fourth, if someone teaches that Christ was a created being but nonetheless one who saved us, then this teaching wrongly begins to attribute credit for salvation to a creature and not to God himself. But this wrongfully exalts the creature rather than the Creator, something Scripture never allows us to do.
From Systematic Theology Second Edition by "Wayne Gruden"