Is prayer going to bring to God's attention a need of which he was not previously aware? Is it going to convince him to do something he was not already going to do? Both of these are impossible with an omniscient deity. On the contrary, if God is all-knowing, he already knows everyone's desires without needing to be told. Likewise, long before any believer ever begins praying for him to take a certain action, his infinite mind will have tabulated every possible reason for or against taking that action, judged the consequences of doing it versus not doing it and run down all the innumerable ramifications of each decision, and finally settled on the verdict that he knows will best achieve his goals. Do theists, believing themselves to be unimaginably small and insignificant by comparison with the Almighty, hope to then change his mind? Do they hope to budge this divine calculus with a single whisper of supplication? A prayer for God to do something he was already going to do is unnecessary; a prayer for God to do something he was not already going to do is futile.