Evan (Steve Carell) is a hard working politician. He sincerely wants to change the world for the best. Just before his first day on the job, he says a quick, innocent prayer asking God to help him "change the world." The rest of the movie is about God's answer to Evan's prayer.
The movie Evan Almighty is loaded with spiritual truth. For example: God hears and answers our prayers. Even better, God answers our prayers with divine extravagance.
God's answers to our prayers stay consistent with His eternal plans. This fact tends to annihilate our own plans (the way we'd prefer things to work out). But this is a good thing because God is eternally smarter than us. For example, when we try to imagine how we might change the world, our minds are limited to small things such as government reform, fundraising and scientific advancement. But God changes the world through drastic, inside-out transformation. He brings the dead back to life, makes the cripple healthy and turns the plans of evil men around for good. We might change the way we look and act, but God changes our very nature.
Evan Almighty demonstrates another truth, that God will teach us the best way to change the world if we ask Him for help. He will stretch us beyond our comfort zones and even our ability to comprehend what's going on to make us useful for His purposes. God's answer to Evan's prayer, for example, did not make him feel more comfortable. When Evan obeyed God he became very unpopular with his colleagues, was ridiculed by the press, almost destroyed his career and almost lost his family.
The writers of Evan Almighty did a masterful job of adapting the Noah story into a modern American scenario. They showed God's utter lack of respect for the pretty buildings and systems that human beings are so impressed with. It was prophetic in its portrayal of our wasteful, American lifestyle in opposition to the natural beauty of God's creation.
The movie also demonstrates how, if we trust and obey God, He will work out all the details. Evan gave up his chances to succeed as a politician in favor of obeying God. Therefore God helped him do his job more effectively than he ever could have imagined. Evan obeyed God even though his family didn't approve. God ended up bringing Evan's family closer than ever. Evan became foolish to everyone who was watching him. Through Evan's foolishness God demonstrated the brilliance of faith.
Evan Almighty does a wonderful job of making people think about God. What else could Christians want? Astoundingly, there are some conservatives (such as James Dobson) who criticized this mainstream movie for not being overtly Christian. This is spiritually shortsighted. Marketing this movie to conservative Evangelicals (for example) would have been the worst thing the makers of Evan Almighty could have done. It is spiritually strategic to lay out God's truth without any religious add-ons. God will uphold His own Truth. His Cause is not helped by our religious insecurities.