Probably few persons are aware that the real meaning of the word _heresy_, after its Greek origin (_hairesis_), means only _opinion_. Heresy consists in the pretensions to explain Holy Scripture after one’s own private judgment or personal opinion instead of receiving the interpretation given to the sacred text by the authority of the Church. Heretics have existed from the time of the apostles. St. Paul, speaking in reference to them, recommends a course which, unfortunately, has not always been followed. “If,” he says, “any man obey not our word, ... have no company with him; ... nevertheless, count him not as an enemy, but admonish him as a brother.” St. Peter, with his zealous ardour, exhorts the faithful, in language full of imagery, to be on their guard against the errors of the Gnostics (that is, the _savants_ or the _érudits_): he calls them “wells without water, clouds that are carried with a tempest.” He then sums up the foundation of their doctrine in a few energetic sentences:--“For when they speak great swelling words of vanity, they allure through the lusts of the flesh, through much wantonness, those that were clean escaped from them who live in error.” We know that the Gnostics believed perfection to consist in science; they held that faith and virtuous living were only meant for the common people. Infatuated by their own learning, they even rejected the authority of Christ, whom they refused to recognise as their Lord and their God; for the doctrine concerning the angels they substituted a theory of divine emanations, and they recognised the ancient doctrine of the eternal antagonism between the good and the evil principle. The Acts of the Apostles, in speaking of the success which attended the preaching of Philip the deacon to the inhabitants of Samaria, relate that there was in that city a magician named Simon, who exercised so great an influence over the people that they all took heed of what he said and called him “the great power of God.” But the miracles worked by Philip had greater influence than the sorceries of Simon, and the people came in crowds to be baptized, Simon himself becoming a disciple of Philip.