So God did truly step into history as Jesus Christ.
However, God did not truly test Abraham and test Isaac, because it’s just way unbelievable that God would send a riddle message and an angel into history.
The ideas folks have in this thread of what is plausible and what is not!
Look, folks. Think about the concept of initiation. God was planning to do something big – to make a covenant with Abraham, to make Abraham’s descendants part of the family of God. This is big freaky stuff. God means people to remember it for thousands upon thousands of years, to burn it into their memory as a people.
If God had just said, “Yo, Abraham! We’re family now!”, would that have been at all impressive and mysterious and worthy of being taken seriously? Nope. The ancient world would have just yawned. Boring. Not even worthy of a story, much less one that would tease people to think about it and retell it until the end of the world.
So yes, I believe God did do this thing, in sober historical fact, on a certain day in an ordinary non-fairy tale place. He was setting up the descendants of Abraham to have a vivid initiatory test and eucatastrophic ending, one where they could identify both with Abraham and Isaac, one that they could argue about for ages over campfires and pixel light. It also served to reinforce God’s lack of desire for human sacrifice, which was a nice lagniappe, and set up the founding of the Temple and all sorts of other things to come.
If ordinary human men can plan out a memorable story setting for their proposals of marriage, I don’t see why people disbelieve that God could and would do the same thing for a proposal and decree of everlasting covenant. If God is the Author of all things, why would you disbelieve His willingness to step in, to set up amazing scenes in real life for pivotal historical events of His people and revelations of Himself?
And contrariwise, if a mere initiatory test of Abraham’s belief in God’s oath that Isaac would live and have descendants – if that seems too dark to be believed, do you really believe that Christ suffered and died and rose again? I mean, wasn’t that awfully masochistic of God, and awfully hard on His poor followers? Surely He should have told Judas not to worry so much, before it fooled the poor guy into suicide. (And so on. Though of course you can avoid all problems with His story by declaring the Gospels fictional, too!)
It’s okay to wrestle with the story of Abraham. Clearly God set up His people to do so, just as He set up Jacob to wrestle in the dark. But declaring the whole thing fictional is a refusal to come to grips with God’s intimate dealings with humanity. Don’t wimp out.