Explain the king's reasoning in Hamlet when he asks, "But, O, what form of prayer can serve my turn?"
In his soliloquy in Act III, Claudius reveals the depth of his weakness and moral corruption. After observing that prayer serves two purposes, to keep us from sin or to pardon us after we have sinned, Claudius asks himself the rhetorical question and then answers it. He cannot pray for forgiveness for murdering Old Hamlet because he still possesses the fruits of his crime--his ambition, his crown, and Gertrude, his queen. There is no prayer for Claudius since he is unwilling to give these up in order to truly repent.
What makes this soliloquy especially interesting is that Claudius is well aware of the state of mortal sin in which he lives:
O wretched state! O bosom black as death!
O limed soul, that struggling to be free
Art more engaged!
He longs for forgiveness, even petitioning the angels to soften his heart and bow his knees, but he will not acknowledge personal responsibility and accept the consequences in order to save his soul. "Pray can I not," he says, hoping foolishly that "[a]ll may be well."