Jesus promised the APOSTLES in John 14 and in John 16 that he would send the Holy Spirit to guide them into ALL truth (obviously spiritual truth), and bring to their remembrance all that he had said to them. In 2 Peter 1:3 Peter said that by the time he wrote that God had granted ALL things that pertain unto life and godliness. So Jesus did what he said he would do. In Jude, verse 3, Jude said that Christians should earnestly contend for THE faith once for all delivered to the saints. (All Christians are saints -- too many passages to cite) Over and over the New Testament writers claimed that the complete gospel was given in the first century. Paul said that if anyone, even himself or an angel from heaven, should preach any other gospel than that which was delivered in the first century, "let him be eternally destroyed." (Galatians 1:6-9) Jesus had earlier said (Matthew 15) that if anyone teaches the traditions of men instead of the teachings of God, that his worship is vain -- useless. The question that Bible believers need to ask and answer is this, "Am I teaching the gospel as found in the scripture, or am I adding to it, deleting from it, or otherwise perverting it?" Along these same lines, Is the Catholic Church, or any other church for that matter, teaching the APOSTOLIC faith or are they teaching the uninspired doctrines of men that originated after the apostles' day? We have no God-given authority to teach anything that is not in the scriptures -- no matter what any council, or synod, or self-styled inspired man may say.
Except for that part where Jesus Himself tells the Apostles "what you loose on earth will be loosed in heaven, what you bind on earth with be bound in heaven..." Did He anticipate them being around for 400 years so they could teach from "scripture"?
You will probably respond that all that the Apostles taught ended up in Scripture, yet John ends his Gospel by pointing out that in no way could he write down all that Jesus did during His ministry.
If Rome cannot affirm the authority of Scripture apart from the caveat that tradition is necessary to explain the Bible's true meaning, let them explain how that does NOT make tradition a superior authority to Scripture.
Since Rome claims infallibility for itself, let them explain how that doesn't make the Scriptures ultimately irrelevant.