Legion tells of God's loss of faith in humanity, so he sends his legion of angels to wipe out the human race for the second time. Mankind's only hope lies in a group of misfits holed up in a diner in the desert who are aided by the archangel Michael.
"When I was a little girl, my mother spoke of a prophecy..."
Actually, voice-over actress woman, I'm thinking your mother spoke of a wicked 1995 movie entitled The Prophecy from which 'Legion' seems to have borrowed a lot, rather blatantly in fact.
"Humans... and how I love you talking monkeys for this... know more about war and treachery of the spirit than any angel."
Rent "The Prophecy".