Justin Martyr, before his conversion to Christianity, tried a number of philosophical schools, landing finally among the Platonists (they required less math than the Pythagoreans). But he still hadn’t found what he was looking for, until he met an old man who pointed him in a different direction. Justin tells of this in a dialogue-within-the-dialogue in his Dialogue with Trypho. For the truth, the old man instructed him to look in the prophetic writings: that is where one finds the truth that saves. Notice that this is in contradistinction to finding a teacher. The old man does not point him in the first instance to another man, but to a book.
Justin: Should any one, then, employ a teacher? Or whence may any one be helped, if not even in them there is truth?
Old Man: There existed, long before this time, certain men more ancient than all those who are esteemed philosophers, both righteous and beloved by God, who spoke by the Divine Spirit, and foretold events which would take place, and which are now taking place. They are called prophets. These alone both saw and announced the truth to men, neither reverencing nor fearing any man, not influenced by a desire for glory, but speaking those things alone which they saw and which they heard, being filled with the Holy Spirit. Their writings are still extant, and he who has read them is very much helped in his knowledge of the beginning and end of things, and of those matters which the philosopher ought to know, provided he has believed them. For they did not use demonstration in their treatises, seeing that they were witnesses to the truth above all demonstration, and worthy of belief; and those events which have happened, and those which are happening, compel you to assent to the utterances made by them, although, indeed, they were entitled to credit on account of the miracles which they performed, since they both glorified the Creator, the God and Father of all things, and proclaimed His Son, the Christ [sent] by Him: which, indeed, the false prophets, who are filled with the lying unclean spirit, neither have done nor do, but venture to work certain wonderful deeds for the purpose of astonishing men, and glorify the spirits and demons of error. But pray that, above all things, the gates of light may be opened to you; for these things cannot be perceived or understood by all, but only by the man to whom God and His Christ have imparted wisdom.
Justin is henceforth converted to the true philosophy, and becomes dependent upon the prophetic and apostolic testimony. Anyone else who desires salvation, he says, should apply himself to the “words of the Saviour”: for they have a “terrible power.”
Justin: When he had spoken these and many other things, which there is no time for mentioning at present, he went away, bidding me attend to them; and I have not seen him since. But straightway a flame was kindled in my soul; and a love of the prophets, and of those men who are friends of Christ, possessed me; and while revolving his words in my mind, I found this philosophy alone to be safe and profitable. Thus, and for this reason, I am a philosopher. Moreover, I would wish that all, making a resolution similar to my own, do not keep themselves away from the words of the Saviour. For they possess a terrible power in themselves, and are sufficient to inspire those who turn aside from the path of rectitude with awe; while the sweetest rest is afforded those who make a diligent practice of them. If, then, you have any concern for yourself, and if you are eagerly looking for salvation, and if you believe in God, you may—since you are not indifferent to the matter —become acquainted with the Christ of God, and, after being initiated, live a happy life.