And he lifted up his eyes and looked, and, behold, three angels in the resemblance of men were standing before him; (angels) who had been sent from the necessity of three things;--because it is not possible for a ministering angel to be sent for more than one purpose at a time;--one, then, had come to make known to him that Sarah should bear a man-child; one had come to deliver Lot; and one to overthrow Sedom and Amorah. And when he saw them, he ran to meet them from the door of the tent, and bowed himself on the earth.
Three Angels, Three Missions — Why Abraham Saw Them at Once
Targum Pseudo-Jonathan on Genesis 18:2