What is meant by the sufficiency of Scripture? How is the Bible sufficient?

TL;DR:

The doctrine of the sufficiency of Scripture states that the Bible is all we need to be equipped for Christian life and service. Scripture reveals who God is, who we are, and how we are to live as those redeemed by God.

what does the bible say?

Scripture is "God-breathed," as the NIV translates it (2 Timothy 3:16), and provides everything necessary to understand God’s will for our lives. God's Word revives the soul, provides wisdom, joy, purity, and endures forever. When we understand that the Word of Scripture is from God Himself and that His ways are far superior to our own ways, we can be sure that Scripture is sufficient for all we need to know God, to understand ourselves, and to know how we are called to live. The doctrine of the sufficiency of Scripture accurately reflects the teachings of Scripture and offers a clear directive for all believers who seek to follow the teachings of the Lord.

from the old testament

Psalm 19:7–9 adds a strong emphasis regarding the sufficiency of Scripture when it states, "The law of the LORD is perfect, reviving the soul; the testimony of the LORD is sure, making wise the simple; the precepts of the LORD are right, rejoicing the heart; the commandment of the LORD is pure, enlightening the eyes; the fear of the LORD is clean, enduring forever; the rules of the LORD are true, and righteous altogether."
Another important aspect of the sufficiency of Scripture is the affirmation that God's ways are superior to our own. Isaiah 55:9 notes, "For as the heavens are higher than the earth, so are my ways higher than your ways and my thoughts than your thoughts." We need God’s Word to know what matters and to understand God’s heart and mind.

from the new testament

The apostle Paul addressed the sufficiency of Scripture in 2 Timothy 3:15–17 when he wrote, "… the sacred writings, which are able to make you wise for salvation through faith in Christ Jesus. All Scripture is breathed out by God and profitable for teaching, for reproof, for correction, and for training in righteousness, that the man of God may be complete, equipped for every good work."
In John 6:63 Jesus tells us about sufficiency: “It is the Spirit who gives life; the flesh is no help at all. The words that I have spoken to you are spirit and life.”
Paul’s words in Galatians 1:8 indicate the seriousness of delivering a message opposed to the truth of God: “But even if we or an angel from heaven should preach a gospel other than the one we preached to you, let him be accursed.”
The Word comes from God Himself and assures us of its sufficiency. “For no prophecy was ever produced by the will of man, but men spoke from God as they were carried along by the Holy Spirit” (2 Peter 1:21).

implications for today

The importance of the sufficiency of Scripture can be seen in many ways because the human tendency is to rely on other solutions to life's problems. Management skills, counseling techniques, and other methods may provide some degree of help, yet only Scripture addresses the ultimate issues of fallen humanity, God's salvation through Jesus Christ, and the principles for Christian living by God's Spirit that allow for living the abundant life (John 10:10). What may appear as the best solution from a human perspective may not always reflect the principles of God's Word. Some of His ways contradict human expectations, such as Jesus teaching that the last shall be first or that the poor in spirit are blessed (Matthew 5:3).

The Protestant Reformation reaffirmed the sufficiency of Scripture in its principle of sola scriptura (Scripture alone), teaching that the Bible alone is necessary to provide the divine words for all of human life. In contrast with the authority of the pope and the many church traditions of that time that were elevated to the level of Scripture or even as more important than Scripture, sola scriptura reclaimed the biblical concept of giving Scripture the highest priority in matters of faith and life. This does not mean information from other fields is unimportant. The Bible does not address every area of life; rather, its revealed words serve as our authoritative source for knowing God, knowing ourselves, and knowing how we are to live in light of that.

Certain worldly methods of drawing crowds, entertainment, extra-biblical revelations, progressive “Christianity,” and some forms of psychological counseling all declare that the Bible is not adequate for the Christian life. But Jesus’ words are “spirit and life” (John 6:63), and they will never pass away (Mark 13:31). His Word is completely and utterly sufficient.

understand

The Bible is "God-breathed" and equips us for faith and life.
Scripture reveals God's wisdom, revives the soul, and guides us in righteousness.
Sola scriptura affirms the Bible as the highest authority for faith and living.

reflect

How has the sufficiency of Scripture impacted your life in a practical way?
In what areas do you tend to seek guidance outside of God's Word, and what role does Scripture play in those areas?
How does understanding the Bible as "God-breathed" influence the way you approach reading and applying it?

engage

How does sola scriptura shape the way we understand truth and authority in the Christian life?
Even in areas where God’s Word does not discuss a topic, what role does Scripture play in our lives?
How can we help others trust in the sufficiency of God's Word when they feel tempted to look elsewhere for guidance, specifically as it relates to who God is, who we are, and how we are to live?