the angel of the LORD: This is the Lord's official messenger. But the term can also refer to other visible signs of the Lord (see Genesis 16:9–13; Judges 13:3, 6, 21–22).
In the Bible, blazing fire often represents God's supreme holiness (see Exodus 19:18; Genesis 15:17; 1 Kgs 18:38–39; Isaiah 33:14).
was not consumed: This may show that God does not want to destroy the object he sets on fire for his purposes.