This is a doctrine that comes into play every day in many ways in our lives. Here is a simple outline, drawn from several sources, of the doctrine.
What does the sufficiency of Scripture mean?
Wayne Grudem gives a good definition: “The sufficiency of Scripture means that Scripture contained all the words of God he intended his people to have at each stage of redemptive history, and that it now contains all the words of God we need for salvation, for trusting him perfectly, and for obeying him perfectly” (Systematic Theology, 127).
The Westminster Confession of Faith says, “The whole counsel of God concerning all things necessary for his own glory, man's salvation, faith and life, is either expressly set down in Scripture, or by good and necessary consequence may be deduced from Scripture: unto which nothing at any time is to be added, whether by new revelations of the Spirit, or traditions of men. Nevertheless, we acknowledge the inward illumination of the Spirit of God to be necessary for the saving understanding of such things as are revealed in the Word: and that there are some circumstances concerning the worship of God, and government of the church, common to human actions and societies, which are to be ordered by the light of nature, and Christian prudence, according to the general rules of the Word, which are always to be observed” (1.6).
Where does the Bible teach this?
a. 2 Timothy 3:15-17 is one key passage.
b. See also Psalm 119:1; Isa 29:13-14; Mark 7:8; 2 Peter 1:16-21; Rev 22:18-19.
c. Hebrews 1:1-4 also has important implications for our understanding. Since God has given the ultimate revelation of himself in his Son, and that revelation is authoritatively recorded only in the Scripture, we need not look elsewhere for understanding God’s redemptive plan.
What are the practical implications of this doctrine?
a. God tells us in the Bible everything we need to know from him about how to think or live.
b. We must not add anything to the Bible.
c. We should not think of any other information as equal to the Bible in truth or authority.
d. God’s requirements for our lives must be defined by the Scriptures, either directly or by good and necessary consequence. We may not call something sin unless we can demonstrate it biblically.
e. In our ethical reasoning, we ought to emphasize what the Scripture emphasizes. Topics and issues in Scripture that are less clear should be lesser in importance to us.
f. We must be content with what God has told us.
What does this doctrine not teach?
a. It does not teach that the Bible is the only factor in making ethical decisions. It teaches that the Bible contains all the divine words that we need. There are other things that we need to live wisely, such as the illumination of the Spirit, correct use of the tools God has given us, and natural revelation.
b. It does not teach that the Bible is the only source of information we may use in decision making.
c. It does not teach that natural revelation is irrelevant. In fact, natural revelation and special revelation must go together. The important point is that special revelation norms or controls our understanding of natural revelation.
d. It does not teach that logic, or right use of reason, is unnecessary. Diligent study and correct reasoning are indispensible to rightly using Scripture.
e. It does not teach that we may not have human teachers, especially those who are well-informed on relevant topics or who are good examples in their wisdom. On the contrary, the Scripture indicates the importance of other people in our discipleship.
f. It does not teach that there are no other legitimate authorities in our lives. In fact, the Bible itself specifically legitimizes other authorities. However, these authorities are always subordinate to the Scripture.
At its heart, this doctrine represents the fact that God alone is the Lord who has ultimate authority.