What Sola scriptura is not.
First of all, it is not a claim that the Bible contains all knowledge. The Bible is not exhaustive in every detail. John 21:25 speaks to the fact that there are many things that Jesus said and did that are not recorded in John, or in fact in any book in the world because the whole books of the world could not contain it. But the Bible does not have to be exhaustive to function as the sole rule of faith for the Church.
Secondly, it is not a denial of the Church's authority to teach God's truth. I Timothy 3:15 describes the Church as "the pillar and foundation of the truth." The truth is in Jesus Christ and in His Word. The Church teaches truth and calls men to Christ and, in so doing, functions as the pillar and foundation thereof. The Church does not add revelation or rule over Scripture. The Church being the bride of Christ, listens to the Word of Christ, which is found in God-breathed Scripture.
Thirdly, it is not a denial that God's Word has been spoken. Apostolic preaching was authoritative in and of itself. Yet, the Apostles proved their message from Scripture, as we see in Acts 17:2, and 18:28, and John commended those in Ephesus for testing those who claimed to be Apostles, Revelation 2:2. The Apostles were not afraid to demonstrate the consistency between their teaching and the Old Testament.
But it is good to be reminded of what SS really is.