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). 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 1:3; see also 2 Thessalonians 2:13-14).

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. 

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.

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 Godly leader “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).