Porphyry (234-305 AD) wrote the Philosophy of Oracles and Against the Christians, both now lost to history. Theodosius II burned all works of Porphyry in 435 and 448 AD, so all that remains are tantalizing fragments quoted by Christian apologists. In other words, what we know about Porphyry comes from his sworn enemies, who rebutted him as they excerpted him.
In Philosophy of Oracles, Porphyry defended the traditional paganism of his day:
“How can these people be thought worthy of forbearance? They have not only turned away from those who from earliest time have been thought of as divine among all Greeks and barbarians… but by emperors, law-givers and philosophers— all of a given mind.
But also, in choosing impieties and atheism, they have preferred their fellow creatures. And to what sort of penalties might they not be subjected who… are fugitives from the things of their Fathers?”
In his fifteen volume Adversus Christianos, Porphyry criticized Christianity for the paucity of its literature, observing that the immature corpus of Christian writings paled in comparison to the oeuvre of paganism. He also distinguished between the original oral traditions of Christianity, straight from the mouth of the Lord, and the subsequent corruption of that doctrine at the hands of the apostles. Keep in mind that Porphyry was writing a mere 300 years after the Crucifixion.
In this fragment, where Porphyry is quoted by St. Augustine (De Civitate Dei, l. xix. cap. 23), the Oracle…
“…The oracle declared Christ to be a most pious man, and his soul, like the soul of other pious men after death, favored with immortality; and that the mistaken Christians worship him.
And when we asked, Why, then, was he condemned? The goddess (Hecate) answered in the oracle: The body indeed is ever liable to debilitating torments; but the soul of the pious dwells in the heavenly mansion.
But that soul has fatally been the occasion to many other souls to be involved in error, to whom it has not been given to acknowledge the immortal Jove.
But himself is pious, and gone to heaven as other pious men do. Him, therefore, thou shalt not blaspheme; but pity the folly of men, because of the danger they are in.”
–From Porphyry, Philosophy of Oracles.
Wilken, R. (1979). “Pagan Criticism of Christianity: Greek Religion and Christian Faith,” in W. Schoedel and R. Wilken, eds., Early Christian Literature and the Classical Intellectual Tradition, pp. 117–134.
Digeser, E. D. (1998). “Lactantius, Porphyry, and the Debate over Religious Toleration,” The Journal of Roman Studies 88, pp. 129–146.