[31] Therefore, also, the servant confirming the fact that he cannot be comprehended who is invisible, and who converses with man invisibly, says, "He is my lord," pointing to Isaac alone. For it is not natural that, if two persons were in sight, he should point to one alone; but the person whom [24] he did not point to, he did not see, inasmuch as he was invisible to all persons of intermediate character.