E.R. Dodds (1893-1979), Pagan and Christian in an Age of Anxiety
(Cambridge: Cambridge University Press, 1965; rpt. 2000), pp. 120-121:
To any one brought up on classical Greek philosophy, pistis meant the lowest grade of cognition: it was the state of mind of the uneducated, who believe things on hearsay without being able to give reasons for their belief. St Paul, on the other hands, following Jewish tradition, had represented pistis as the very foundation of the Christian life. And what astonished all the early pagan observers, Lucian and Galen, Celsus and Marcus Aurelius, was the Christians' total reliance on unproved assertion—their willingness to die for the indemonstrable.1 For Galen, a relatively sympathetic observer, the Christians possess three of the four cardinal virtues: they exhibit courage, self-control and justice; what they lack is phronesis, intellectual insight, the rational basis of the other three.2 For Celsus they are the enemies of science: they are like quacks who warn people against the doctor, saying that knowledge is bad for the health of the soul.3 Later on Porphyry seems to have repeated the same protest against 'an irrational and unexamined pistis'; and Julian exclaims, 'There is nothing in your philosophy beyond the one word "Believe!"'4
1 Lucian, Peregr., 13, Christian beliefs unsupported by evidence; Galen, De puls. diff., 2.4 (III, 579 Kühn), Jews and Christians obey undemonstrated rules; Celsus apud orig., c. Cels.. 1.9, 6.11, some Christians say, 'Ask no questions; just believe'; M. Ant., 11.3.2. Christians are ready to die, not on any reasoned ground but out of sheer contrariness (κατὰ ψιλὴν παράταξιν). Cf. Walzer's discussion in Galen, pp. 48-56.
2Galen in Walzer, Galen, p. 15 (the passage survives only in Arabic quotations); discussion, ibid., pp. 65-74.
3 C. Cels., 3.75.
4 Porph., Adv. Christ., fr. 1.17 (cf. fr. 73); Julian apud Greg. Naz., Orat., 4.102 (P.G. 35, p. 637).