"Abraham saw my day"

56 Your father Abraham rejoiced that he would see my day. He saw it and was glad.” 57 So the Jews said to him, “You are not yet fifty years old, and have you seen Abraham?” 58 Jesus said to them, “Truly, truly, I say to you, before Abraham was, I am.” 59 So they picked up stones to throw at him, but Jesus hid himself and went out of the temple (Jn 8:56-59).

What does v56 refer to? Does it denote Abraham's prophetic anticipation? Does it allude to Abraham in paradise? A problem with those interpretations is that Jesus goes onto to indicate, quite provocatively, that he was a contemporary of Abraham at the time Abraham was still alive. Indeed, that he preexisted Abraham. So that wouldn't refer to the heavenly Abraham, but the historical Abraham. An incident in the earthly life of Abraham.  

I think the best candidate is to view Gen 18:2,13 as a Christophany. Even in the original setting, there's a theophanic angelophany. Of the three visitors, two are angels, while the third is Yahweh, in human appearance. That identification would be consistent with other passages in the Fourth Gospel, like Jn 12:41, which posits another Yahwistic Christophany.