An Afternoon Prayer (and question)

We bumped into this prayer the other day, which brings up angels. Here’s the prayer, and then a question:

O God, who in a wonderful order has established the ministry of Angels and of men, mercifully grant that even as Your holy Angels ever do You service in heaven, so at all times they may defend us on earth. Through our Lord. Amen.

Do you believe in angels? Why or why not? Any experiences to tell?