E. DePalma Digeser, Lactantius, Porphyry, and the debate over religious toleration, The Journal of Roman Studies 88 (1998) 129 – 146:
Lactantius also appears to respond more broadly to Porphyry’s portrayal of Jesus as a divine, pious sage. Hierocles had quite a different view: Jesus was a robber, a magician, and a second-rate miracle-worker who set himself up as a god. Apart from Hierocles’ thoroughgoing comparison of Jesus with Apollonius –which Lactantius suggests is the main thrust of his work and Eusebius considers to be unique– the rest of his material seems to derive from Celsus who also treats Jesus as a wicked sorcerer and a liar. Porphyry, conversely, considers Jesus to be a wise and pious sage– and he emphasizes his uniqueness by introducing the oracle in praise of Christ with the words: “What I am about to say may actually seem surprising: The gods have proclaimed that Christ was extremely devout and become immortal…”. As Wilken has shown, Lactantius was clearly aware of Porphyry’s arguments concerning the divinity of Christ. But Lactantius himself may have moved toward Porphyry on this issue, since his own Christology is, like Eusebius’, almost Arian in nature: his Christ has a substantia between God and human beings. Moreover, the Divine Institutes strongly emphasizes Jesus’ role as a wise teacher (doctor sapientiae).
Porphyry may also have opened himself u[ to a charge of hypocrisy by advocating continence without practicing it: he had urged his students tp lead a life of sexual abstinence in De abstinentia, yet had then seemingly ignored his own teaching by marrying Marcella. His protestations in the Ad Marcellam, in fact, indicate that he had been accused of marrying her in order to have both children and comfort in his old age.
Marcella’s wealth is also relevant to several of Lactantius’ criticisms. One who praises frugality can easily be accused of avarice for marrying a wealthy woman. Marcella’s money may also explain the snide observation that Lactantius’ philosopher ate better at home than in the palace. Finally, Marcella’s property may relate to the accusation that the philosopher lobbied judges unscrupulously. […] The philosopher was looking for judicial help in keeping property for which people close to him thought they had claim. Indeed, Porphyry and Marcella may have encountered opposition from men who sought to gain her property through marriage.
Since Marcella was a recent widow, certain people in the community, who had designs on her wealth, may have similarly threatened Porphyry with legal action or with physical punishment. If Marcella really were Jewish, that circumstance may have also elitited opposition from her ‘fellow-citizens’. Perhaps Porphyry’s notorious interest in Chaldaean theurgy was enough to expose him, like Apuleius, to a similar accusation of black magic.
It thus seems reasonable to conclude that before 303 Porphyry went to Nicomedia to attend Diocletian’s conference, called to lay the groundwork for the Great Persecution. When he was there he presented not Against the Christians, a long, scholarly work that would have been unsuitable for reading aloud in public, but his Philosophy from Oracles.
Valerian’s son Gallienus had decided to allow Christian worship in some form, and Diocletian himself had promoted Christians to important positions, including the chair in Latin rhetoric that Lactantius occupied. Diocletian’s later decision to persecute certainly furthered his goal of uniting a long-divided empire around the new tetrarchic theology of rule. Nevertheless, to justify such a dramatic change of policy after a half-century of accommodation, the emperor may have needed to appeal to a respected authority on religion. Porphyry’s Philosophy from Oracles thus may have given Diocletian a philosophical basis for persecuting Christians