Orthodoxy and Heresy
If indeed growing in knowing doctrine is important, if indeed growing in the knowledge of God is growing in knowing doctrine, then wrong doctrine is very serious. Heresy and wrong doctrine basically is a distortion of the true knowledge of God. Instead of having our minds transformed by the renewing of our minds (c.f. Rom. 12:2), heresy and wrong doctrine distorts our perception of God and of the faith.
Now, the first thing we note is that in the Scriptures, there is present one deposit of truths about God. The most common objection normally to sound doctrine is the relativization of all interpretations of all Scripture, and thus making Scripture wholly subjective. In the minds of such people, you have "your interpretation" and I have "my interpretation" and who are you or anyone else to say who's right and who's wrong?
The problem with this objection is that it denies what Scripture teaches. Scripture is not clay to be molded into anything anyone wants. For example, does anyone want to claim that "Jesus did not die on the cross" is a valid interpretation of Scripture at all? I certainly hope not.
The Scriptures speak of "the faith once for all delivered to the saints" (Jude 3). It speaks of the pattern of sound words (2 Tim. 1:13). It speaks of the tradition handed down by the apostles (2 Thess. 3:6). There is therefore such a thing as a body of fixed truths handed down to us, and these objective truths are for us to discover and understand and mine for. We are not to ignore them or relativize them.
Since there is such a thing as a fixed pattern of sound words, therefore, there is such a thing as orthodoxy (right teaching). Anything that contradicts this orthodoxy is either heresy or wrong teaching, depending on the nature of the truth that it contradicts.
What does all this have to do with us? If we call ourselves Christians therefore, we are to love God and His Word and the doctrines of Scripture. Therefore, we are to hate heresy and false teaching because they contradict God's truth. We are to hate it because heresy and false teaching destroys souls. It causes professing believers to fall away, and ruins their spiritual lives and witness for Christ.
If we detest rapists and murderers because they hurt or ruin others, why then do we not detest the spiritual rapists and murderers? Our priorities seemed to be way off when we regard the former as worse than the latter. The first can only destroy the body; the second destroy both the body and the soul. As Jesus said,
And do not fear those who kill the body but cannot kill the soul. Rather fear him who can destroy both soul and body in hell. (Mt. 10:28)
Let us therefore learn to hate heresy and wrong teaching at least just as much if not more than physical rapists and murderers. Let us treasure sound doctrine and hate false ones.