Brutha is the Chosen One.
His god has spoken to him, admittedly while in the shape of a tortoise.
Brutha is a simple lad. He can't read. He can't write. He's pretty good at growing melons. His wants are few.
He wants to overthrow a huge and corrupt church. He wants to prevent a horrible and holy war. He wants the persecution of a philosopher who has dared to suggest that, contrary to the Church's dogma, the Discworld really does go through space on the back on an enormous turtle* He wants peace and justice and brotherly love. He wants the Inquisition to stop torturing him now, please. But most of all, what he really wants is for his god to choose Someone Else . . .
*Which is true, but when has that ever mattered?