Excuse this long post, but its from the 3rd century philosopher Porphyry, who wrote a multi volume text attacking the Christian faith on theological, rational, scientific etc, grounds. Of course almost all of it was burned by the Roman church, but some fragments remain, of which this following passage explains many of them:
The "end" of knowledge is truth, though one could also call it a "god." This "god" is not the Christian god, nor even the Christian idea of God. Theologians from the second century onward had misread Plato (and would later misread Plotinus and Porphyry) on this fundamental point." page 159
"Porphyry's "God," therefore, has no need to save because he is not affected by sin. This is not to say that the philosopher fails to recognize a category of actions which are displeasing to God. But these actions are expressions of active failure and not of a passive genetic deficiency in a God-created race of men, as Augustine theorized. God strengthens those who practice virtue and "noble deeds" (Marcella 16), but he does not (cannot) punish those who fail to practice virtue or who do things contrary to virtue (Marcella 17), since the divine nature can only work for the good. Accordingly, the classical Christian theodicy does not arise in Porphyry's thought; he thinks it foolish to speculate, on Christian premises, about an all-good God, creator of an originally good world, over which, through lack of foresight (omniscience) or power (omnipotence) evil reigns and in which he is obliged to intervene time and time again. The puzzles of Christian theology are non-puzzles for Porphyry: The pieces comprise not a picture but a muddle, and can only be slotted together by trimming edges and omitting embarrassingly contorted segment. This, however, does not prevent Christian priests and teachers from selling their wares as a kind of philosophy. While religious observances -pagan or Christian - are not actually harmful, they encourage the simple-minded in a belief that God has need of them. The only true priests are the wise of the world, not the "fools praying and offering sacrifice". The only truly sinful man is "he who holds the opinions of the multitudes concerning God" (Marcella 17), and those who think that tears, prayers, and sacrifices can alter the divine purpose. The Christian god fails, in Porphyry's view, because he epitomizes false opinion, baseless hopes. He is changeable, fickle, unpredictable. His priests preach "mere unreasoning faith [in a God] who is gratified and won over by libations and sacrifices," without perceiving that men making exactly the same request receive different answers to their prayers (Marcella 23). Worse, human beings seem to believe that their basest actions can be erased by prayer, or, caught in the web of their illogic, they become haters of the world and the flesh and mistakenly accuse the flesh of being the source of all evil (Marcella 29). "Salvation" for Porphyry cannot begin with self-hatred or the abnegation of the flesh. In its demythologized form, it is simply the "soul's" quest for wisdom as expressed in the pursuit of virtue - an acknowledgment of redemption being natural to the soul because of the soul's affinity to God. Porphyry does not think of the body as vile; he thinks of it as the discardable "outer man," whose satisfaction cannot be a final end or goal because it is corruptible, limited, and earthbound. The body defines creaturely existence and not the soul's quest." pages 162-164