In order to obtain a more perfect initiation and a less fragmentary insight into the doctrines taught by the Oriental religions, we are compelled to turn to two kinds of testimony, inspired by contrary tendencies, but equally suspicious: the testimony of the philosophers, and that of the fathers of the church. The Stoics and the Platonists frequently took an interest in the religious beliefs of the barbarians, and it is to them that we are indebted for the possession of highly valuable data on this subject. Plutarch's treatise _Isis and Osiris_ is a source whose importance is appreciated even by Egyptologists, whom it aids in reconstructing the legends of those divinities.[20] But the philosophers very seldom expounded foreign doctrines objectively and for their own sake. They embodied them in their systems as a means of proof or illustration; they surrounded them with personal exegesis or drowned them in transcendental commentaries; in short, they claimed to discover their own ideas in them. It is always difficult and sometimes impossible to distinguish the dogmas from the self-confident interpretations which are usually as incorrect as possible. The writings of the ecclesiastical authors, although prejudiced, are very fertile sources of information, but in perusing them one must guard against another kind {15} of error. By a peculiar irony of fate those controversialists are to-day in many instances our only aid in reviving the idolatry they attempted to destroy. Although the Oriental religions were the most dangerous and most persistent adversaries of Christianity, the works of the Christian writers do not supply as abundant information as one might suppose. The reason for this is that the fathers of the church often show a certain reserve in speaking of idolatry, and affect to recall its monstrosities only in guarded terms. Moreover, as we shall see later on,[21] the apologists of the fourth century were frequently behind the times as to the evolution of doctrines, and drawing on literary tradition, from epicureans and skeptics, they fought especially the beliefs of the ancient Grecian and Italian religions that had been abolished or were dying out, while they neglected the living beliefs of the contemporary world.