Good topic, and one I have often wondered about. The answer I found was, that in reference to "YHVH hardened his heart.." is better understood as YHVH "strengthened" his heart. In other words, Pharaoh's hearts desire was to do exactly as he did...yet he lacked the resolve to follow thru. Much as when one has labored over a task with desire to finish, but has run out of steam and must rest before continuing. (my conclusions based on possible translations of "harden" from the Hebrew -and other places those words were used)