You have to remember that Christians believe in the Trinity, that's God in 3 persons. Sort of like water in three forms- solid, liquid, and gas. They're all H20 but can exist in 3 forms and that's what Christians believe about God. So to say that you can and can't see God face to face are both true for Bible believing Christians.

When I was a Christian, hearing other Christians use this analogy made me want to throw things. It’s NOT representative of the doctrine of the Trinity. It actually reduces to non-Trinitarian modalism. The same water does not normally exist in all three states at the same time. According to Chalcedonian Trinitarianism, he Father, Son and Holy Spirit are three distinct persons of one substance/essence at the same time. The analogy fails.

That said, the overall “solution” to the contradiction you pose is indeed one that Christians often use going back at least to Justin Martyr and Tertullian.

There are several problems with saying that every visible manifestation of god in the OT was actually a Christophany, however. If the god substance is invisible, what makes the Son manifestation of it visible? If it’s merely his human nature that makes him visible, then people aren’t really seeing god, are they?

It also creates a myriad of problems when people go back and look at the OT and try to determine when "YHWH" is referring to the Father, the Son or all of the Trinity. Additionally, all the supposed Christophanies have to be read back into the OT text which creates some really weird situations like in Daniel chapter 7, where Daniel supposedly sees a vision of the “Ancient of Days” (the Father?) and “one like a son of man” (the Son?) come up to him. How did he see both?

Perhaps the better way around the contradiction is by playing with the meanings of words like of “seeing” and “invisible”. IOW, the passages in the NT that speak of god being invisible just mean that he’s not visible at present and the Johannine passages that speak of nobody having seen god really just means that nobody has fully understood/comprehended god, not that nobody has seen some sort of visible manifestation of god. It was solutions like this that Augustine proposed and other systematic theologians have developed since.