This is another one I always enjoy, though I admit it's largely a monotheist / Abrahamic question. If your version of god is all knowing, and has a plan, what would be the point of prayer? If, for example, you have a relative who gets diagnosed with an illness, would you pray for them to get better? It seems praying for god to do his will is pointless, he's going to do it anyway. If you're praying for the illness to cure, aren't you asking god to change his plan? If you don't expect him to change his plan, and he's going to either cure or not cure anyway, aren't you hoping the unchangeable god changes its mind? I guess I just don't understand how this is supposed to work. Of course if you think god can change his mind, or that he doesn't have a full plan< i get that praying would seem like a sensible idea, but otherwise I don't get it.
I limit it to intercessory prayer, but if you like, some people think prayer is simply to praise his name. Why does god need or want people to do that?