God spoke to Moses and said to him, "I am the Lord. I appeared to Abraham, to Isaac and to Jacob, as God Almighty, but by my name the Lord I did not make myself known to them."
"But," he said, "you cannot see my face, for man shell not see me and live."
The Claim: God can't appear to people because if they see God's face, they would die, yet God appeared to Abraham, Isaac, and Jacob.
The Explanation: To explain this, we need only to answer the question, "Is it possible to appear to someone and not show your true face?" The answer is yes, of course. It is very possible to appear to someone and not show them your face. We can even verify this because people can do this. Turn on the news and watch for a bank robbery that's been caught on tape. The bank robbers are usually wearing some sort of a ski mask to cover up their face. Did the bank robbers appear at the bank? Yes, of course. Did people see their faces? No, their faces were covered up behind ski masks.
In a similar way, God can appear to people without showing His face. In fact, God does this a number of times in the Bible. Take for instance Deuteronomy 31:15, where God appeared to people in a pillar of cloud. They did not see God's true face, they saw God appearing as a pillar of cloud. This is not a contradiction.