'Angel of the Lord' in the Bible

And the Angel of the LORD found her beside a fountain of water in the wilderness: even by a well in the way to Shur.

And the Angel of the LORD said unto her, "Return to thy mistress again, and submit thyself under her hands."

And the angel of the LORD said unto her, "I will so increase thy seed, that it shall not be numbered for multitude."

Then the angel of the LORD called unto him from heaven saying, "Abraham, Abraham?" And he answered, "Here am I."

And the angel of the LORD cried unto Abraham from heaven the second time,