Clement of Alexandria (d. ca 215) is the first Christian author to have discussed matters of knowing reality with any consistency. For him, Christian knowledge has to embrace God, the universe, and everything else, with theology in its highest form being open at both ends, namely, towards the creator and the creation. This chapter begins by discussing Clement’s complex, interdisciplinary representation of reality, including the primary element of this method, the ‘holy gnostics.’ It continues by addressing the figure of Abraham as an accomplished ‘gnostic,’ an astronomer and a theologian, and it ends by suggesting lessons for contemporary conversations between scientists and theologians.