May I suggest (under the guidance of the Apostolic Scriptures) that the Memra of YHVH appeared to Avram in such a way as to allow Avram to address him as a servant would address his earthly master in respect? Did Avram see a man? Did he see the LORD? I can't be dogmatic either way. But one thing is sure: Avram believed the unbelievable, but it was to the Word of the LORD, the Memra, that he addressed his objective faith! Surely HaShem saw into the heart of the patriarch and recognized the appropriation of the choices that lay before him. What is more, only the LORD himself can supernaturally open the eyes of a man to allow him to make a choice between choosing his Messiah or rejecting him. Avraham chose to lay hold of the Promise given in Genesis 12:1-3 by seeing at the heart of such a promise a glimpse of the Messiah who would bring it to pass!