The Latin expression “sola scriptura” refers to the authority of the Holy Scriptures to serve as the sole norm for all that is taught and confessed in the church. In numerous passages the Scriptures claim this authority for themselves as the inspired Word of God. For example, St. Paul writes in 2 Tim. 3:16, “All scripture is inspired by God and profitable for teaching, for reproof, for correction, and for training in righteousness…” (RSV). Likewise, the apostle Peter declares that “no prophecy of scripture is a matter of one’s own interpretation, because no prophecy ever came by the impulse of man, but men moved by the Holy Spirit spoke from God” (2 Pet. 1:20-21; RSV). It should be remembered that acceptance of the Bible as the sole authority for teaching comes not from rational arguments or human traditions, but is a conviction produced by the Holy Spirit in the human heart. In other words, it is a matter of faith worked by the Holy Spirit through the Scriptures themselves (see 1 Thess. 2:13)!
There is, of course, no contradiction between 2 Pet. 1:20 and what Peter says later in 3:15-16. That the Scriptures may be difficult for human beings to understand in certain places does not take away from their divine authority. In fact, St. Peter’s words underline the necessity and importance of praying for the Holy Spirit’s guidance to properly interpret Scripture as we “grow in the grace and knowledge of our Lord and Savior Jesus Christ” (2 Pet. 3:18; emphasis added).
Hope this helps…