'Angel of the Lord' in the Bible

And as he was revolving the matter in his mind, behold, an angel of the Lord in a dream appeared unto him, saying, Joseph, son of David, fear not to take Mary for thy wife, for that which is conceived in her is from the Holy Spirit.

Then Joseph when arisen from sleep, did as the angel of the Lord commanded him, and took his wife;

Now when they were gone, behold an angel of the Lord appeared unto Joseph in a dream, saying, Arise, and take the infant and his mother by night, and flee into Egypt, and stay there, till I speak to thee, for Herod will search for the infant to destroy it.

Now when Herod was dead, behold, the angel of the Lord appeared in a dream to Joseph in Egypt,

And, lo! there was a great earthquake; for an angel of the Lord descending from heaven, came and rolled back the stone from the door, and sat upon it.