5 Καὶ ἔστιν αὕτη ἡ ἀγγελία ἣν ἀκηκόαμεν ἀπʼ αὐτοῦ καὶ ἀναγγέλλομεν ὑμῖν, ὅτι ὁ θεὸς φῶς ἐστιν καὶ σκοτία ἐν αὐτῷ οὐκ ἔστιν οὐδεμία. 6 Ἐὰν εἴπωμεν ὅτι κοινωνίαν ἔχομεν μετʼ αὐτοῦ καὶ ἐν τῷ σκότει περιπατῶμεν, ψευδόμεθα καὶ οὐ ποιοῦμεν τὴν ἀλήθειαν· 7 ἐὰν ἐν τῷ φωτὶ περιπατῶμεν ὡς αὐτός ἐστιν ἐν τῷ φωτί, κοινωνίαν ἔχομεν μετʼ ἀλλήλων καὶ τὸ αἷμα Ἰησοῦ τοῦ υἱοῦ αὐτοῦ καθαρίζει ἡμᾶς ἀπὸ πάσης ἁμαρτίας. 8 ἐὰν εἴπωμεν ὅτι ἁμαρτίαν οὐκ ἔχομεν, ἑαυτοὺς πλανῶμεν καὶ ἡ ἀλήθεια οὐκ ἔστιν ἐν ἡμῖν. 9 ἐὰν ὁμολογῶμεν τὰς ἁμαρτίας ἡμῶν, πιστός ἐστιν καὶ δίκαιος, ἵνα ἀφῇ ἡμῖν τὰς ἁμαρτίας καὶ καθαρίσῃ ἡμᾶς ἀπὸ πάσης ἀδικίας. 10 ἐὰν εἴπωμεν ὅτι οὐχ ἡμαρτήκαμεν, ψεύστην ποιοῦμεν αὐτὸν καὶ ὁ λόγος αὐτοῦ οὐκ ἔστιν ἐν ἡμῖν. (1 John 1:5-10 NA28)
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 translated from the NA28 Greek text)
The following definition for the word “esoteric” is from the New Oxford American Dictionary:
intended for or likely to be understood by only a small number of people with a specialized knowledge or interest : esoteric philosophical debates.
esoterically |-(ə)lē| adverb
esotericism |-ˈterəˌsizəm| noun
esotericist |-ˈterəsist| noun
ORIGIN mid 17th cent.: from Greek esōterikos, from esōterō, comparative of esō ‘within,’ from es, eis ‘into.’ Compare with exoteric .
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 are 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.