The biblical doctrine of Sola Scriptura, that Scripture alone is the only ultimate and infallible authority over the Church and every Christian, rests on the fact that Scripture is Godís perfect Word. The Bible says that Godís Word is perfect. His Word is complete. His Word is breathed out by the Holy Spirit.
We know that words can sometimes be misunderstood, but we still function in our day-to-day lives assuming that words communicate fairly well. While we may occasionally need to clear up misunderstandings, we do not ordinarily need to stop and form elaborate study committees to exegete all of our conversations. While Godís Word has the kind of depth and richness that invites further study Ė like great literature and poetry always does, it also remains clear and straightforward in all of its essentials. The Bible clearly explains that God created the world, that people sinned and rebelled and were estranged from God, but that God determined to rescue humanity beginning with the family of Abraham and his covenant relationship with Israel. This culminated in Jesus Christ, Godís own Son, who lived a perfect life, was betrayed and executed and who rose from the dead three days later, ascended into heaven, and poured out His Spirit on all who believe, establishing Christís body, the Christian Church. The Bible clearly sets out the forgiveness of our sins in the blood of Christ, the promise of that forgiveness in baptism, and the fellowship in that grace through the bread and wine shared at communion. The Bible clearly describes the work of the Holy Spirit in a believer, conforming them into the image and likeness of Jesus because when someone becomes a Christian, Christ begins to live inside of them, giving them new desires to love and obey God.
All of this is clearly set forth in Scripture. There are sometimes difficult passages and things that are difficult to understand, but this does not mean that the Bible is not clear about the central things, the most important things. Rather, the Bible is Godís Word to man, and God does not mumble. He has spoken clearly so that we might know Him and walk with Him.