ANSWER: Have no fellowship with those teachers, who deny the very fundamentals of Christianity, such as the reality of Christ's body, making it a phantom, a sham, as in verse 7; for such a religious leader "is a deceiver and an antichrist." Both the first and second epistles of John are aimed directly at this gnostic error called docetism. Its teachers were not only false in faith, but corrupt in morals, not fit to be entertained by any Christian family. To sympathize with such leprous leaders is to become "a partaker in their evil works." The idea of leadership is in verse 9 correctly translated, "whosoever goeth onward" (R. V.) as a teacher, or leads others, etc.
— Steele's Answers p. 163, 164.