And it is good to remember that all of us can be guilty of heresy at some time in our life. This is simply due to sin, our pride, lack of knowledge or misguided ideas. Our only hope is Christ crucified and the mercy of God. This is one of those reasons we must be sure to forgive. We all need to be forgiven of something, and as God is all good we surely can’t pretend that any sin we commit is of no consequence.
I think one of the points being made through Paul’s interactions with the Galatians, is we can get so wrapped up in rules, laws and regulations that we forget “the spirit of the law.” and thus become to self righteous and judgmental. What can follow next is becoming a heretic. I could be wrong, but I have thought this myself.