'Angel of the Lord' in the Bible

But while he was thinking on these things, behold an angel of the Lord appeared to him in a dream, saying, Joseph, thou son of David, fear not to take to thee Mary thy wife; for that which is begotten in her, is of the Holy Ghost.

Then Joseph, being raised from sleep, did as the angel of the Lord had bidden him, and took unto him his wife:

And when they were gone back, behold an angel of the Lord appeareth to Joseph in a dream, saying, Arise and take the young child and his mother, and flee into Egypt, and continue there till I shall tell thee; for Herod will seek the young child to destroy him.

But when Herod was dead, behold an angel of the Lord appeareth in a dream to Joseph in Egypt,

And behold, there had been a great earthquake, and an angel of the Lord descending from heaven, had come and rolled away the stone from the door and sat upon it.