Why does the importance of the doctrine of the Trinity even matter? Well, because just about everything that matters in Christianity hangs on the truth of God’s three-in-oneness. Take the supreme issue of our sin which separates us from God and renders us subject to his wrath. Theologian, Bruce Milne, wrote: “In the final analysis sin concerns two parties, the offending sinner (us) and the offended God. Hence, if Jesus [is only a man and] is not God, well then my sin really has nothing to do with him.

Once when Jesus forgave a man’s sins he was accused of blasphemy, for only God can forgive sins (Mark 2v5-7). In one sense his critics were perfectly correct; their error lay in not seeing who Jesus was. – Only if Jesus is God come to us in person can he deal with our sins; and conversely, if he deals with our sins, then He must be God.”

Bruce Milne, 1982, Know The Truth, IVP Leicester, p.62-63