http://www.christianfaith.com.au/resour ... nt-go-away
Many authors emphasise the dangers of Gnosticism. ‘This was a heresy far more subtle and dangerous than any which hitherto appeared’ (Renwick); ‘insidious enemy’ (Prof. Jackson); ‘the greatest of the philosophical threats’ (Cairns) are just 3 authors who paint a picture of a fierce enemy.
There is much debate, still, as to whether the infant church fought Gnosticism. Some see evidence of anti-Gnostic teaching in Paul’s letters to Corinth, Galatia and Colossae. However, the debate continues with many ‘ifs’ and ‘buts’. I merely mention it. There is a stronger case for John’s first epistle. Some even venture to suggest that John’s Gospel was written to counter early Gnostic teaching. Maybe so; maybe not. It has been mainly R. Bultmann and his followers who ‘believe they can detect both direct and indirect references to Gnosticism in the NT, especially in the writings of John and Paul.’ (8)