The mortal sin of heresy in Scripture

Updated: Jan 2

By Luke Lancaster


If somebody falls into heresy, they commit a mortal sin. Paul spoke of this in Galatians 5 when he wrote to the Galatian Christian community about how, if they believed in the false teaching that circumcision brought salvation, that they would be cut off from God. Such a heretical belief prompted him to say that they were “severed from Christ” (Gal. 5:4).


Believing in this one false teaching prompted Paul to say that. We might think that simply believing in something false is not a big deal, however, think about how we act as Americans when somebody openly believes in racism. We stop associating with that person. They are severed from us.


So also Christ, if we believe something that contradicts His official teachings in His Church, makes Him not want to associate with us. Now, to expand on the Galatian Christians, they believed that circumcision brought salvation because they were being persuaded by a group of Jewish agitators. Those agitators were claiming that circumcision indicated one’s membership in the Covenant of God’s people.


Now, this idea used to be true under the old Covenant, but Paul had made it clear that the action was not needed anymore with the coming of Christ. Circumcision was a ceremony that was not needed to enter Heaven, for with the coming of Christ, all that was needed was faith “working in love” (Gal. 5:6). We need to be a disciple of Jesus, believing in His love and truths, and living out His life.


That’s what indicates Covenant membership, not circumcision. So, because of that false teaching, Paul says to the Galatians, “You are severed from Christ, you who would be justified by the law; you have fallen away from grace” (Gal. 5:4). The Galatian Christians had committed a mortal sin.