About 9 years ago I had another pastor in town come to see me about particpating in a city wide prayer vigil. Sounded like a good idea, then He said "God needs our help in defeating Satan." Really, God needs our help?
Let's see, Jesus said if we won't worship him, even the stones would (Luke 19:40), if we won't speak for God, even a donkey will (Numbers 22:28), and if we don't obey, a fish is ready to do the Lord's work (Jonah 1:17).
That's what we find in Chapter 5, God fought His own battle against the Philistine people and their god Dagon without help from the Israelite army. Because of their disobedience, God's people missed out on the help they could have had.
God will do it with or without you, no one is indispensable.
God is not privileged when we serve Him.
It is our privilege to get to serve Him!