Origen wrote about many branches of theology, including textual criticism, biblical exegesis and hermeneutics, philosophical theology, preaching, and spirituality. Some of his teachings, however, quickly became controversial. Notably, he frequently referred to his hypothesis of the pre-existence of souls. In the beginning all intelligent beings were united to God. In his writingas, Origen also considered the possibility, that in the end all beings, perhaps even the arch-fiend Satan, would be reconciled with God in what is called the apokatastasis ("restitution"). 