He next proceeds to recommend, that in adopting opinions we should follow reason and a rational guide, since he who assents to opinions without following this course is very liable to be deceived. And he compares inconsiderate believers to Metragyrtæ, and soothsayers, and Mithræ, and Sabbadians, and to anything else that one may fall in with, and to the phantoms of Hecate, or any other demon or demons. For as among such persons are frequently to be found wicked men, who, taking advantage of the ignorance of those who are easily deceived, lead them away whither they will, so also, he says, is the case among Christians.
And he asserts that certain persons who do not wish either to give or receive a reason for their belief, keep repeating, “Do not examine, but believe!” and, “Your faith will save you!” And he alleges that such also say, “The wisdom of this life is bad, but that foolishness is a good thing!” To which we have to answer, that if it were possible for all to leave the business of life, and devote themselves to philosophy, no other method ought to be adopted by any one, but this alone.
For in the Christian system also it will be found that there is, not to speak at all arrogantly, at least as much of investigation into articles of belief, and of explanation of dark sayings, occurring in the prophetical writings, and of the parables in the Gospels, and of countless other things, which either were narrated or enacted with a symbolic signification, (as is the case with other systems). But since the course alluded to is impossible, partly on account of the necessities of life, partly on account of the weakness of men, as only a very few individuals devote themselves earnestly to study, what better method could be devised with a view of assisting the multitude, than that which was delivered by Jesus to the heathen?
And let us inquire, with respect to the great multitude of believers, who have washed away the mire of wickedness in which they formerly wallowed, whether it were better for them to believe without a reason, and (so) to have become reformed and improved in their habits, through the belief that men are chastised for sins, and honoured for good works or not to have allowed themselves to be converted on the strength of mere faith, but (to have waited) until they could give themselves to a thorough examination of the (necessary) reasons.
For it is manifest that, (on such a plan), all men, with very few exceptions, would not obtain this (amelioration of conduct) which they have obtained through a simple faith, but would continue to remain in the practice of a wicked life. Now, whatever other evidence can be furnished of the fact, that it was not without divine intervention that the philanthropic scheme of Christianity was introduced among men, this also must be added. For a pious man will not believe that even a physician of the body, who restores the sick to better health, could take up his abode in any city or country without divine permission, since no good happens to men without the help of God.
And if he who has cured the bodies of many, or restored them to better health, does not effect his cures without the help of God, how much more He who has healed the souls of many, and has turned them (to virtue), and improved their nature, and attached them to God who is over all things, and taught them to refer every action to His good pleasure, and to shun all that is displeasing to Him, even to the least of their words or deeds, or even of the thoughts of their hearts?
Source: Against Celsus (New Advent)