Is the Bible a sole rule of faith (sola scriptura)?
The Catholic Church takes the position that tradition and Scriptures are equally valid sources of revelation. It further takes the position that the final authority on scriptural interpretation is the teaching magisterium of the church, which resides in the bishops, councils and ultimately, the bishop of Rome.
The Protestant groups nearly all tend to disregard tradition and cling only to the Bible. They endeavor to let the Bible explain itself when mysteries are encountered. If you recall, Jesus did rebuke the religious leaders of His day over this point (see Mark 7:7-9).
Yet Malachi Martin, in his book "The Keys of This Blood," states that the Roman church takes the position that each Protestant group tries to explain the Bible as they see it and thus they make themselves gods.
A word of warning
Probably one of the great errors made by so-called students of the Word is that they begin their study with preconceived ideas, and then go to the Bible to confirm them. Far better to get the cart and the horse reversed and go to the Bible first for the principles of life. Then evaluate their life and with God's help make the needed alterations.
2 Timothy 3:16 explains that the entire Bible is God-breathed and is useful for teaching, rebuking, correcting and training in righteousness, so that the man of God may be thoroughly equipped for every good work. Though this does not say that the Bible is the sole rule of faith, it is clear that it will thoroughly equip a person with faith which results in every good work. Thus, there is no need to find other books or people to give us a rule of faith for it has all been provided in the Bible. Furthermore the Bible warns against accepting rules taught by men and gospels other than those preached in the Bible. (Mark 7:6-8; 2 Corinthians 11:4; Galations 1:6-9)
Why does 2 Thessalonians 2:15 refer to an oral tradition? If you go to the original language of the New Testament, Greek, the word tradition here means 'things delivered, handed over, or transmitted by way of teaching or doctrine'. The prominent idea of the word is one of authority above that of the teacher; therefore, here it refers to inspired messages received by Paul and his companions and faithfully passed on to the Thessalonians.
In 1 Corinthians 11:2 Paul is referring to the regulations he had given the Corinthians concerning public worship and private conduct. He did not preach the gospel to them and then leave them to formulate their own rules of church order and social life. He did thorough work in the churches that he established, and gave instruction that enabled the new Christians to be confident in their worship and in their daily lives that they were living according to the will of their Lord (see 1 Corinthians. 4:17; 7:17; 2 Thessalonians 2:15). By so doing he left an example for all ministers of the gospel to follow. Converts to the faith should be thoroughly instructed concerning all phases of church activity and the affairs of social and domestic life, in order that they may be sure that they are carrying out the desires of the Lord for their well-being in all respects.
The oral "traditions" (or better, "teachings") of Paul and his associates in the ministry, are what these two texts refer to.