The New International Version Study Bible says that Gnosticism was "one of the most dangerous heresies of the first two centuries of the church" (page 1,906, Introduction to 1 John, article "Gnosticism").
Q. I am a subscriber member and have heard (not sure of the spelling) Naustisism, Naustic, mentioned in a couple of sermons in a negative way, and am embarrassed to admit I have no idea what it is.
A. Thank you for your E-mail with your question from some of the sermons you have heard. I believe the concept you are asking about is "Gnosticism" or the "Gnostic" school of thought. Please don't be embarrassed to ask! The word is not in common use these days, and so it is not particularly unexpected that you have not run across it.
The name comes from the Greek word gnosis, which means "knowledge." Vine's Complete Expository Dictionary of Old and New Testament Words defines it as "primarily a seeking to know, an enquiry, investigation" (page 348).
Unfortunately, the Gnostic school of thought went far beyond the simple definition of the word. The New International Version Study Bible says that Gnosticism was "one of the most dangerous heresies of the first two centuries of the church" (page 1,906, Introduction to 1 John, article "Gnosticism"). That is most certainly true.
Its core teaching could be described as what we call "dualism"—in this case, the teaching that spirit is entirely good and matter is entirely evil. From this idea, Gnostics concluded several things, chief among them the idea that man's body, since it is matter, is evil (contrast this to Genesis, where God said that everything He made was "very good").
They also claimed that salvation was attained by escaping the body through special knowledge (hence the term "Gnosticism"), which included worship of angels (this is undoubtedly what Paul referred to in Colossians 2:18-23). They denied that Christ had actually come in the flesh (since they believed all matter was evil, they thought the Son of God couldn't have really been a human being)—a claim that would mean we have no Savior, since He gave His life to pay for our sins.
One form of Gnosticism held that the body was to be treated harshly (since it was matter, and therefore evil)—contrast that to Paul's exhortation to glorify God in our bodies, since the body is the temple of God's Holy Spirit (1 Corinthians 6:19-20). Gnostics of this particular "brand" were ascetic, reclusive and lived like hermits. Another form of Gnosticism, in a strange twist of reasoning, held that since it was matter that was evil or sinful (not the breaking of God's law—1 John 3:4), it didn't matter what a person did in the flesh because only the spirit was important! These types of Gnostics led wild, licentious, unrestrained lives. What a mess!
Hopefully this gives a little context to the messages you have heard, and the references to this particular heresy that Paul, John and other of the early apostles had to battle against. This subject is also addressed in a couple of our booklets: Sunset to Sunset—God's Sabbath Rest page 42 and God's Holy Day Plan page 60. If you need free copies of these booklets, just let us know, or you can find them in the literature library of our Web site at https://www.ucg.org.au/library.