Well, time out. Who was the man Abraham ate with? So, if the Lamb of God was slain before the foundation of the world, couldn't Jesus as God also be the Son of God (God the Son) and the Son of Man?
Throughout the Tanakh and the New Testament, angels seem to have the ability to appear as men. Does this mean angels are men? No. It means that they can temporarily appear as men to us. I don't think that He is a man in Heaven until after the cross, though He might have the appearance of a man, which might explain how God makes us in His image--though I think making us in His image has another meaning, not a physical one.
I believe that Jesus was the "man" that Abraham ate with, that Joshua encountered near Jericho, and that went through the fire with Meshach, Shadrach, and Abed-Nego. But I don't believe He was a fleshly man until the virgin birth.
I can't find your reference to the Lamb of God being slain before the foundation of the world. My understanding is that the Lamb of God was slain on the cross. (Perhaps you are getting two different verses confused? Let me know. I really couldn't find your reference.) Jesus certainly existed before the foundation of the world, but not, I think, as a man. The whole point of the virgin birth and the incarnation of Christ is that He entered the world as a true man of flesh for the first time.
Do you understand all of this differently?
DO you think I am going to read my bible and twist it to fit someone elses interpretation, 321 I think is the right reference to keep someone busy explaining.
Read it backwards: Come quickly Lord Jesus or vice versa. In the beginning He was and is already there.