Questioning those within Christianity who advocate doctrine that denies the benchmark doctrines we have been given is not an enjoyable activity. It involves a lot of work and research and it must be done in a manner which does not bring discredit to our Lord. This requirement, to remain objective and avoid insults is extremely difficult because it can easily involve emotions where one’s character or intentions are called into question. Nevertheless, when false doctrines and unbiblical practices are encountered, it is required. The following is a direct copy and paste from gotquestions.org. It answers the “why” factor but it does not address the “how” factor. Of these two factors, I think the “how” factor is the most difficult. Exchanging polite dialogue with someone who is supportive of a doctrine or practise you are questioning requires the ability to make your case without demeaning the individual to whom you are speaking with. I’ve addressed this topic previously in a post that provides additional information here: https://bcooper.wordpress.com/2018/06/09/why-is-sound-doctrine-so-important/ Maybe I will address that “how” aspects at a later point in time. In the interim, here are the basics with regard to “why” sound doctrine is important.
Sound doctrine is important because our faith is based on a specific message. The overall teaching of the church contains many elements, but the primary message is explicitly defined: “Christ died for our sins according to the Scriptures [and] . . . he was raised on the third day according to the Scriptures” (1 Corinthians 15:3-4). This is the unambiguous good news, and it is “of first importance.” Change that message, and the basis of faith shifts from Christ to something else. Our eternal destiny depends upon hearing “the word of truth, the gospel of your salvation” (Ephesians 1:13; see also 2 Thessalonians 2:13-14).
Sound doctrine is important because the gospel is a sacred trust, and we dare not tamper with God’s communication to the world. Our duty is to deliver the message, not to change it. Jude conveys an urgency in guarding the trust: “I felt I had to write and urge you to contend for the faith that was once for all entrusted to the saints” (Jude 1:3; see also Philippians 1:27). To “contend” carries the idea of strenuously fighting for something, to give it everything you’ve got. The Bible includes a warning neither to add to nor subtract from God’s Word (Revelation 22:18-19). Rather than alter the apostles’ doctrine, we receive what has been passed down to us and keep it “as the pattern of sound teaching, with faith and love in Christ Jesus” (2 Timothy 1:13).
Sound doctrine is important because what we believe affects what we do. Behavior is an extension of theology, and there is a direct correlation between what we think and how we act. For example, two people stand on top of a bridge; one believes he can fly, and the other believes he cannot fly. Their next actions will be quite dissimilar. In the same way, a man who believes that there is no such thing as right and wrong will naturally behave differently from a man who believes in well-defined moral standards. In one of the Bible’s lists of sins, things like rebellion, murder, lying, and slave trading are mentioned. The list concludes with “whatever else is contrary to the sound doctrine” (1 Timothy 1:9-10). In other words, true teaching promotes righteousness; sin flourishes where “the sound doctrine” is opposed.
Sound doctrine is important because we must ascertain truth in a world of falsehood. “Many false prophets have gone out into the world” (1 John 4:1). There are tares among the wheat and wolves among the flock (Matthew 13:25; Acts 20:29). The best way to distinguish truth from falsehood is to know what the truth is.
Sound doctrine is important because the end of sound doctrine is life. “Watch your life and doctrine closely. Persevere in them, because if you do, you will save both yourself and your hearers” (1 Timothy 4:16). Conversely, the end of unsound doctrine is destruction. “Certain men whose condemnation was written about long ago have secretly slipped in among you. They are godless men, who change the grace of our God into a license for immorality and deny Jesus Christ our only Sovereign and Lord” (Jude 1:4). Changing God’s message of grace is a “godless” thing to do, and the condemnation for such a deed is severe. Preaching another gospel (“which is really no gospel at all”) carries an anathema: “let him be eternally condemned!” (see Galatians 1:6-9).
Sound doctrine is important because it encourages believers. A love of God’s Word brings “great peace” (Psalm 119:165), and those “who proclaim peace . . . who proclaim salvation” are truly “beautiful” (Isaiah 52:7). A pastor “must hold firmly to the trustworthy message as it has been taught, so that he can encourage others by sound doctrine and refute those who oppose it” (Titus 1:9).
The word of wisdom is “Do not remove the ancient landmark which your fathers have set” (Proverbs 22:28, NKJV). If we can apply this to sound doctrine, the lesson is that we must preserve it intact. May we never stray from “the simplicity that is in Christ” (2 Corinthians 11:3).