Dean Winchester complains—infrequently, because it is in his nature to be glad of what is his, not to covet what is not his, but he does complain—that the world abounds with bad things happening to good people and with evildoers running amuck, that it is the seventh day and God is resting (in Tijuana with tequila and a hot senorita, Dean says, but Castiel has looked and God is not there) and God never checks his voicemail. But Dean himself is the one spoken of by age-old revelation from a prophet of God—Jophiel, Habakkuk, John, Chuck—the one who will end this evil, or lock the worst of it away for another age as did Yeshua ben Maryam when angels last walked the earth (but not so many Seals had opened when Michael restored them through Yeshua).
Dean Winchester does not believe there is a God, and for a long time he believed there never was; if Dean had any sense of self-worth, it would be worth telling him (because then he might believe) that the only reason Castiel still believes there is a God is because God gave him Dean Winchester.