Heresy
as it it used here,
comes from the Greek, meaning,

Disunion; division; sect.
Heresy came to mean, "A fundamental error
in religion, or an error of opinion respecting
some fundamental doctrine of religion."
Since we now have so many different
Christian churches, what is sound
doctrine in one church may be 'heresy'
in another; presumably a very
good reason why God advised
us against disunion, and  
different sects in the  
first place.   

Now the works of the flesh are manifest,
which are these;
Adultery, fornication, uncleanness, lasciviousness,
Idolatry, witchcraft, hatred, variance, emulations,
wrath, strife, seditions, heresies,
Envyings, murders, drunkenness, revellings, and such like: of the which I tell you before,
as I have also told you in time past,
that they which do such things
shall not inherit
the kingdom of God
Galatians   
5:19-21