William Blake’s theology is expressed in a strange, idiosyncratic idiom that is difficult to pin down. Sometimes Blake is even read as an anti-Christian, proto-Nietzschean thinker. However, in 1910, Chesterton noted Blake’s unusual ‘tenderness’ toward the Catholic faith and even suggested that he was already on the path toward Catholicism. In this paper, I present an interpretation of Blake’s theology, focusing on his early work The Marriage of Heaven and Hell and on the ‘fetters’ that he attributes to Milton, implying that he is free of them. I argue that Blake is a sincere Christian – and, as Chesterton suggested, far closer to Catholicism than one might expect. Blake’s profound and insightful reflection on the epistemological and psychological effects of original sin forge a middle way, akin to that of Catholicism, between a ‘Pelagian’ belief in the ability of human beings to redeem themselves through their own efforts and a Calvinist insistence on humanity’s total postlapsarian depravity.