I can only think of one other time that Angels were mentioned in this show. It was the episode where the people were killing people who were intending on doing something evil. Do you remember what that episode was?

This is the episode where we learn Dean doesn't believe in God. Sam tells Dean he prays and has faith. Dean tells Sam that Mary used to tell him as a boy that 'angels were watching over us', but Dean believes she was wrong and that there was no higher power protecting her from dying.

The priest shows them a painting of the archangel Michael. He says a Scripture often calls angels as God's warriors.