There can be no doubt that when different people use the word “God” they mean different things (or persons). Atheists deny that there is “God” but even they aren’t necessarily asserting the non-existence of the same entity. Equally it is clear that for someone who is a Christian of an orthodox, especially an orthodox Calvinist, type, someone could believe in and even worship a “god” without knowing or worshipping the God Christians worship. “Idolatry”, the worship of a false (probably non-existent) god was a real and intense worry for Calvin and his successors.
From that point of view one might say that for such a Christian God functions as a name, a proper noun, and hence its capitalisation. God for such a one (God for me) is a person in this very direct and immediate sense. God has a name, can be recognised or mis-recognised. This raises two questions by analogy: could one fail to recognise God when one met God? could one mistake someone (or thing) else for God? The answer to both these questions (for me) is yes.
The next question is whether and how this matters and to whom. Does it matter that some fail to recognise God (and I’ll say this includes all atheists)? Assuming that God wants all to know God then those who say they don’t must have failed, somehow, to see what’s going on, whether wilfully or not (leaving aside for the moment vexed questions of election, which might lead one to think the decision here was God’s). This is an interesting question but not the one I’m dealing with here.
The other question is: does it matter that some who believe themselves to know God are actually mistakenly using that word (name) to identify something else (probably something they have created or imagined themselves)?
This, I think, is the problem of heresy. To say that a belief is heretical means, primarily, that someone is using the word God intending to name the God revealed in Jesus but actually pointing to some other entity. The belief so described is one that hides our God (Father, Son and Holy Spirit, three in one and one in three) by putting something else between us and God.
Some will deny that God can be hidden by mere false belief but I really think that this can happen. Christianity is a revealed religion. This means that we think that knowing God can’t occur without God’s initiative. God has to show us what God is, we can’t work it out for ourselves. The form this revelation takes is Jesus, and Jesus as revealer of God can only be understood as the culmination of the story of Israel. God is not knowable to us except through Jesus, who was and is both God and man.
Heresies obscure this in one way or another. I’m inclined to the view that all heresies, ultimately, are, in the jargon, Christological. They are heresies because they prevent us from maintaining the mystery of man and God united in a single person who is both absolutely human and completely God. Once we lose sight of this we cease to be able know the God revealed in and as Jesus.
Here “know” is ambiguous and difficult. When we “know” someone this doesn’t mean that we know things about them, nor that we become capable of coming up with descriptions or explanations that fully account for or capture who they are and the things they do. It means we recognise them and are recognised by them. That a relationship between us exists with patterns and mutual expectations. This is what it means, it seems to me, for us to “know” God.
Our systems of theology are part of this, in a way analogous to the stories we tell ourselves and others about the people we know. They help us to orient ourselves, to remember and to understand, in some degree, these people. Heresies. though, play a malign role in that they are like lies and falsehoods people tell us about those we know. They give us false ideas and false expectations and make us relate to God as if God were the distorted image they convey.
The conclusion from this is that theology is mostly about avoidance of false ideas rather than the development of true ones. The truest idea about someone won’t hugely enhance ones relationship with them (it will make some difference but try having a real conversation with someone you’ve only read about) but one lie can destroy it, if its bad enough.
The big problem is knowing which are those really bad falsehoods and what one should do about them.