The New Testament epistles are basically defense against an array of Gnostic ideas and philosophies. Paul's epistle to Colossians is the most outstanding rebuttal of Gnosticism! His preaching in Athens (Acts 17) illustrates to us the battles this apostle had against the Gnostics of his day.

The apostle John is no less important to understand the fact that Gnostics subverted the true original Church from within. John wrote his Gospel and his epistles toward the end of the 1st century. He was an eyewitness to the fact that the original apostolic Church was now infested with Gnosticism to the point of no return.