The New Testament link between heresy and the demonic was not lost in the post-apostolic period, even if such language sounds strange to our ears today.
Certainly, for Paul, the instability caused by the deceitful schemes of men, that the maturing Ephesian Church needed to grow out of, were not unrelated to the schemes of the devil (Eph. 4:14; 6:11). He is even more explicit about the connection in 1 Timothy 4 and 2 Corinthians 11.
Jaroslav Pelikan saw this as an implication of the renouncing of the devil by candidates for baptism.
"...it is evident already from such New Testament terminology as 'deceitful spirits and doctrines of demons' that 'the devil, and his pomp, and his angels,' disowned by the candidate for baptism as part of the sacramental ritual of initiation, are seen as the instigators not simply of the worship of the false gods of paganism outside the church but of the false teachings and 'the godless chatter and contradictions of what is falsely called knowledge' within professedly Christian ranks.
Renouncing the devil means denouncing heresy--not only one's own, if any, but anyone else's, past, present or future."
Pelikan, Credo, p. 191-2