Tatian, a second-century Assyrian Christian and pupil of Justin Martyr before becoming an Encratitic rigorist, is known for his Oratio ad Graecos (“Address to the Greeks”), an early Christian apology, as well as his (now lost) Diatesseron, a harmony of the four Gospels.
In the Oratio, Tatian gives an account of his conversion and provides us with another answer to the question of where one goes when one wishes to know what Christians believe. That is to say, Tatian tells us he was converted by reading “certain barbaric writings” which led him to conclude that the Christian faith was the true faith. Indeed, he lists a number of criteria by which he judges (you know, personally or privately) that Scripture is superior to the writings of the pagans–for when he reads them, his soul is “taught of God” and he “put[s] faith” in what he reads.
Wherefore, having seen these things, and moreover also having been admitted to the mysteries, and having everywhere examined the religious rites performed by the effeminate and the pathic, and having found among the Romans their Latiarian Jupiter delighting in human gore and the blood of slaughtered men, and Artemis not far from the great city sanctioning acts of the same kind, and one demon here and another there instigating to the perpetration of evil,–retiring by myself, I sought how I might be able to discover the truth. And, while I was giving my most earnest attention to the matter, I happened to meet with certain barbaric writings, too old to be compared with the opinions of the Greeks, and too divine to be compared with their errors; and I was led to put faith in these by the unpretending cast of the language, the inartificial character of the writers, the foreknowledge displayed of future events, the excellent quality of the precepts, and the declaration of the government of the universe as centred in one Being. And, my soul being taught of God, I discern that the former class of writings lead to condemnation, but that these put an end to the slavery that is in the world, and rescue us from a multiplicity of rulers and ten thousand tyrants, while they give us, not indeed what we had not before received, but what we had received but were prevented by error from retaining. (Oratio ad Graecos 29)