Let us, then, turn to his services as theologian and philosopher. He wrote over a thousand treatises, and on almost every subject that has interested the human mind; but his labors were chiefly confined to the prevailing and more subtle and dangerous errors of his day. Nor was it by dry dialectics that he refuted these heresies, although the most logical and acute of men, but by his profound insight into the cardinal principles of Christianity, which he discoursed upon with the most extraordinary affluence of thought and language, disdaining all sophistries and speculations. He went to the very core,--a realist of the most exalted type, permeated with the spirit of Plato, yet bowing down to Paul. We first find him combating the opinions which had originally enthralled him, and which he understood better than any theologian who ever lived. But I need not repeat what I have already said of the Manicheans,--those arrogant and shallow philosophers who made such high pretension to superior wisdom; men who adored the divinity of mind, and the inherent evil of matter; men who sought to emancipate the soul, which in their view needed no regeneration from all the influences of the body. That this soul, purified by asceticism, might be reunited to the great spirit of the universe from which it had originally emanated, was the hopeless aim and dream of these theosophists,--not the control of passions and appetites, which God commands, but their eradication; not the worship of a Creator who made the heaven and the earth, but a vague worship of the creation itself. They little dreamed that it is not the body (neither good nor evil in itself) which is sinful, but the perverted mind and soul, the wicked imagination of the heart, out of which proceeds that which defileth a man, and which can only be controlled and purified by Divine assistance. Augustine showed that purity was an inward virtue, not the crucifixion of the body; that its passions and appetites are made to be subservient to reason and duty; that the law of temperance is self-restraint; that the soul was not an emanation or evolution from eternal light, but a distinct creation of Almighty God, which He has the power to destroy, as well as the body itself; that nothing in the universe can live without His pleasure; that His intervention is a logical sequence of His moral government. But his most withering denunciation of the Manicheans was directed against their pride of reason, against their darkened understanding, which led them not only to believe a lie, but to glory in it,--the utter perverseness of the mind when in rebellion to divine authority, in view of which it is almost vain to argue, since truth will neither be admitted nor accepted.