Please summarize "Batter my heart."
This poem is, of course, a prayer to God. In it, the speaker is asking God to make him (the speaker) good -- to make him the way God wants him to be.
In this poem, the speaker has decided that he, by himself, cannot be what God wants him to be. He is not strong enough, himself, to break away from Satan. Because of this, he wants God to force him to be good.
You can see this in the images he uses. He asks God to "batter" or break down his heart -- to be forceful. He asks God to defeat him like a town that is taken in battle. He even asks God to "ravish" him -- a word that usually was used to mean rape.
So this speaker is asking God to take control of his life and save him from his own bad ways.