A doctrine can only be considered truly biblical when it is explicitly taught in the Bible. An issue could be unbiblical (opposed to the teachings of the Bible), extra-biblical (outside of or not mentioned in the Bible), biblically based (connected to the teachings of the Bible), or biblical.
An unbiblical doctrine is any teaching that stands opposed to the Bible’s clear teaching. For example, a belief that Jesus sinned is unbiblical. It stands in direct contrast to what the Bible teaches in many places, including Hebrews 4:15: “We have one who has been tempted in every way, just as we are—yet he did not sin.”
An extra-biblical doctrine would be any teaching that is not directly taught in the Bible. It can be either good or bad. For example, voting in a democratic election is a positive practice, but it is not explicitly commanded in the Bible. To observe certain holidays is often neither good nor bad: “One person considers one day more sacred than another; another considers every day alike. Each of them should be fully convinced in their own mind” (Romans 14:5). Any teaching about the observance of Lent, for example, is extra-biblical.
Other teachings can be based on biblical principles, yet not directly taught in the Bible. For example, smoking is never mentioned in the Bible. Yet we can assert that the practice should be avoided, based on 1 Corinthians 6:19-20, “Your body is a temple of the Holy Spirit within you. . . . You are not your own, for you were bought with a price. So glorify God in your body.” When a biblical principle applies, we can confidently teach it as a biblically based doctrine.
Biblical doctrines, then, are teachings explicitly taught in the Bible. Examples of these include God’s creation of the heavens and earth (Genesis 1:1), the sinfulness of all people (Romans 3), the virgin birth of Jesus (Matthew 1:20-25; Luke 1:26-38), the physical death and literal resurrection of Jesus (1 Corinthians 15:3-11), salvation by grace alone through faith alone (Ephesians 2:8-9), the inspiration of Scripture (2 Timothy 3:16-17), and many others.
Problems occur when people confuse these categories. For example, to teach that the virgin birth is an optional doctrine that Christians are free to believe or not believe is to reject a core teaching of the Bible. It presents a biblical doctrine as non-essential. Then there are those who present extra-biblical teachings as if they were biblical doctrines. A person’s opinions and preferences are given the weight of God’s law; this happens sometimes in matters of clothing, music style, and food choice. When we “teach as doctrines the commandments of men” (Mark 7:7), we become like the Pharisees whom Jesus strongly condemned.
Our goal must be to speak clearly and firmly when Scripture is plain. In extra-biblical matters, we must be careful to avoid dogmatism. As many have said, in the essentials unity; in the non-essentials, diversity; in all things, charity.