Exodus 23: 20 - 22
20 "Behold, I send an angel before you, to guard you on the way and to bring you to the place which I have prepared.
21 Give heed to him and hearken to his voice, do not rebel against him, for he will not pardon your transgression; for my name is in him.
22 "But if you hearken attentively to his voice and do all that I say, then I will be an enemy to your enemies and an adversary to your adversaries.

EWTN