Doctrine is a set of accepted beliefs held by a particular group. In Christianity, it is the set of true beliefs that define the parameters of our belief system. Consequently, there is true doctrine and false doctrine relative to each belief set. For example, within Christianity, a true Biblical doctrine is that there is only one God in all existence (Isaiah 43:10, 44:6, 8). A false doctrine is that there is more than one God in all existence.
This major_christian_doctrines link provides a PDF list of the basic major doctrines of the Christian faith that are accepted by all Protestant denominations that are considered Christian, should you wish to peruse them. Bear in mind that there are a good number of other subjects within our Bible that are also important such as our understanding of the end times, the Law of Moses and the covenants etc.
Understanding the doctrines of the Bible is a skill set that is quickly diminishing within the body of Christ, the Church. The reasons for this are varied but paramount among the reasons is a basic lack of knowledge or familiarity with God’s Word. In order to be able to recognize a teaching that is not in accordance with God’s Word, it is necessary to be conversant with what God’s Word teaches on a given doctrine. If you’re reading something in a book or listening to a podcast or watching a video, we need to be able to have a standard to which we can compare it with to discern as to whether what is being taught is in line with God’s Word. If you aren’t conversant with God’s Word, then you have nothing to compare it with and are more subject to being mislead.
“Discernment is not knowing the difference between right and wrong. It is knowing the difference between right and almost right.” ~ C. H. Spurgeon
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 1:3; 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, a man who believes in well-defined moral standards will have a tendency to conduct himself differently from one who believes in no standard or accountability. 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).
Worthy is the Lamb! Blessings!