The Clarity, Necessity, and Sufficiency of the Bible

Clarity of Scripture
   The Bible speaks of its own clarity and of the responsibility of believers to read and understand it. God expected that all His people would know and be able to talk about His Word with proper application to ordinary life situations.

Why do people misunderstand Scripture?
   The problem always lies not with Scripture but with ourselves. People through their own "short comings" misunderstand what is clearly written in Scripture. As people grow in the Christian life, gaining more knowledge of Scripture as they spend time studying it, will understand better.

The Necessity of Scripture
   1). The Bible is necessary for the knowledge of the Gospel; 2). The Bible is necessary for maintaining spiritual life; 3). The Bible is necessary for knowing God's will

Can people who don't read the Bible know anything about God?
  Yes! People can obtain a knowledge that God exists and a knowledge of some of His attributes simply by observing of themselves and the world around them. "The heavens declare the glory of God; And the firmament shows His handiwork." (Ps. 19:1) The consciences of unbelievers bear witness to God's moral standards, but at times this evidence of God's law on the hearts of unbelievers is distorted or suppressed. (Rom. 2:14-15)
  The above describes "general revelation." General revelation comes through observing nature, through seeing God's directing influence in history, and through an inner sense of God's existence and his laws that he has placed inside every person.  Nowhere does Scripture indicate that people can know the Gospel or the way to heaven through general revelation. Special revelation is needed. Special revelation refer to God's words addressed to specific people, such as the words of the Bible, the words of the Old testament prophets and New testament apostles, and the words of God spoken in personal address, such as at Mount Sinai or at Jesus' baptism.
It is great wonder of our redemption that God himself has provided the way of salvation by sending his own Son, who is both God & man, to be our substitute and bear the penalty for our sins, combining the "justice and love" of God in one infinitely wise and amazingly gracious act!

Notes taken from Wayne Grudem's "Bible Doctrine."