5 And this is the message, which we have heard from him and we proclaim to you, that God is light and there is not any darkness in him. 6 If we say that we have fellowship with him and walk in darkness, we lie and are not practicing the truth. 7 But if we walk in the light as he is in the light, we have fellowship with one another and the blood of Jesus his son cleanses us from every sin. 8 If we say that we do not have sin, we deceive ourselves and the truth is not in us. 9 If we confess our sins, he is faithful and righteous, that he may forgive us our sins and cleanse us from all unrighteousness. 10 if we say that we have not sinned, we make him a liar and his word is not in us. (1 John 1:5-10 Possessing the Treasure New Testament V1)
The following definition for the word “esoteric” is from the New Oxford American Dictionary: (See the definition on the site)
Not long after God had mercy on me in January 1986, saving me, I remember seeing a newspaper ad with the title “Esoteric Christianity” in bold letters. Below that in nearly as large bold letters was one word, “Gnosticism.” There was a phone number below that. I was a new believer, but I had heard in a Bible study about Gnosticism and how it was a heresy. What is a heresy?
“Error, indeed, is never set forth in its naked deformity, lest, being thus exposed, it should at once be detected. But it is craftily decked out in on attractive dress, so as, by its outward form, to make it appear to the inexperienced (ridiculous as the expression may seem) more true than truth itself.” Irenaeus Against Heresies 1.2
In other words, a heresy is something false that is portrayed or taught as the truth in such a way that is very convincing to professing believers who are not very mature and have not been trained to be discerning.
What is it that makes Gnosticism a heresy? As the definition for the word “esoteric” above tells us, it was a religious mysticism that pirated Christian motifs to propagate a totally unchristian understanding of salvation than what we know of in our Orthodox Christian faith. In Gnosticism, salvation is based on esoteric “knowledge” (Greek γνῶσις or gnōsis). To the Gnostic, redemption is through affirming the divine light already in the human soul, not through repentance of sin and faith in Christ’s death to bring about spiritual rebirth.