Now, you are just contradicting yourself. Before you said "becoming God" is a euphemism for unity but now, you're full on buying into the literal man-is-god thesis.
The bottom line is that you put no weight on the words of Jesus or Scripture and fully weigh the words of the early church fathers. I'm the opposite. I hold Scripture to be the inspired word of God and where anyone contradicts - or goes beyond - that is given zero weight.
8 No matter the source of the false gospel, even if it is preached by us or a heavenly messenger, ignore it. May those who add to or subtract from the gospel of Jesus be eternally cursed! 9 Listen again: if anyone preaches to you a gospel other than what you have accepted, may he find himself cursed!Galatians 1:8-9
Therefore, going to back to this thread's title, "Why Christ's Deity is important;' is invalid. Scripture does not say Christ is a deity, let alone that this is important.
He explained his views--- He said clearly that he regards it as union with God, rather than becoming God. Did you miss that, or are you just ignoring that he said that.
How do you understand John 14:15-20 ?