Neoplatonism was a major influence on Christian theology throughout Late Antiquity and the Middle Ages in the West. This was due to St. Augustine of Hippo, who was influenced by the early neoplatonists Plotinus and Porphyry, as well as the works of the Christian writer Pseudo-Dionysius the Areopagite, who was influenced by later neoplatonists, such as Proclus and Damascius. Early Christians including Origen, Gregory of Nyssa, and Augustine were influenced by Neoplatonism, but none accepted it uncritically and they rejected absolute monism and its emanationists' views. Certain central tenets of Neoplatonism served as a philosophical interim for the Christian theologian Augustine of Hippo on his journey from dualistic Manichaeism to Christianity. As a Manichee, Augustine had held that evil has substantial being and that God is made of matter; when he became a Neoplatonist, he changed his views on these things. As a Neoplatonist, and later a Christian, Augustine believed that evil is a privation of good and that God is not material. Perhaps more importantly, the emphasis on mystical contemplation as a means to directly encounter God or the One, found in the writings of Plotinus and Porphyry, deeply affected Augustine. According to his own account of his important discovery of 'the books of the Platonists' in Confessions Book 7, Augustine owes his conception of both God and the human soul as incorporeal substance to Neoplatonism. But Augustine was also critical of Neoplatonism doctrines and their formulations, and he rejected the Neoplatonists' immaterialism. Other Christians assimilated Neoplatonist ideas, especially in their identifying the Neoplatonic One, or God, with Yahweh. The most influential of these would be Origen, who potentially took classes from Ammonius Saccas (but this is not certain because there may have been a different philosopher, now called Origen the pagan, at the same time), and the late 5th century author known as Pseudo-Dionysius the Areopagite.