Genesis 18:8

And he took butter and milk and the calf which he had dressed, and set it before them; and he stood by them under the tree, and they did eat. Although the meal was simple, it was plentiful. Abraham himself did not sit down with his guests, but stood in order to wait upon them and carry out their slightest wish. The eating of physical food on the part of the heavenly beings was a true partaking of the meal, something like that of the resurrected Christ, Luke 24:41 ff.; but it remains a miracle to our comprehension. The entire incident pointed forward to the time when the Son of God visited His people, lived among them, and, above all, let them see His kindness and His love.