According to Protestants, every Christian doctrine must be derived from Scripture alone. Any doctrine or practice that is not explicitly stated in the Scriptures is rejected as "unbiblical". Because of this, Sacred Tradition, say Protestants, is not a legitimate source of truth, and was never meant to be, and therefore, what is not in the Bible is likewise not true.
Protestants attempt to support sola scriptura by making references to the greatness and authority of "God's Word", or the "Word of the Lord", as it is found in many places throughout the Bible. The problem is, the "Word of the Lord", in Scripture, almost always meant oral preaching (Is. 55:10-11; Ps. 119:89; Acts 13:49) rather than the Bible, which was not yet compiled. In 1 Peter, we see that the "Word" is nothing more than "the good news that was announced to you" (1 Pet. 1:25). The Scriptures are indeed the "word of God" (John 10:35), but the "word of God" is not restricted to the Bible alone. The "word of God" is contained in both written and in unwritten forms.
Protestants use various Biblical passages to support sola scriptura. Their favorite is 2 Timothy 3:16: "all Scripture is inspired by God and is profitable for doctrine, for reproof, for correction, and for training in righteousness, so that the man of God may be competent, equipped for every good work." Notice Paul uses the word "profitable" (ophelimos) and not "sufficient", the same words used in Titus 3:8 to describe "good deeds." Of course, Protestants would not agree that good deeds are sufficient for salvation. Further, Protestants conclude from the passage that Scripture will equip the Christian "for every good work." Notice that in 2 Timothy 2:21, cleansing from all that is unholy will prepare him "for every good work." James 1:4 says that "perseverence" will "complete" the believer so that he is "lacking in nothing." The fact is, Scripture is "useful" and contributes, along with other things, to doctrine, correction, and training in righteousness. These things–doctrine, reproof, correction, and righteousness, (to which Scripture contributes, but not exclusively so) are what makes a person "equipped for every good work." As for 2 Timothy 3:15: "And that from infancy you have known [the] sacred scriptures, which are capable of giving you wisdom for salvation through faith in Christ Jesus," Paul is saying that the Scriptures are capable of giving wisdom unto salvation, but not necessarily the Scriptures alone.
Protestants also cite Acts 17:11: "Upon arrival they went to the synagogue of the Jews. These Jews were more noble than those in Thessalonica, for they received the word with all willingness and examined the Scriptures daily to determine whether these things were so." The Protestant claim has always been that the Bereans believed in Sola Scriptura, because they were allegedly subordinating the teachings of the Apostles to the Scriptures. But of course, this makes sense. The passage tells us that they "searched the Scriptures," and then became believers. They did not uphold their private interpretation of the Scriptures while refusing to submit to the authority of the Apostles because they were good Christians, but because they had not yet accepted the authority of Christ and his Magesterium. Once they accepted the teachings of the Apostles, they submitted to their authority. The Bereans first received the word by oral tradition, and then accepted the word because their teaching was consistent with, and proved by, Scripture. After all, if something contradicts Scripture, it must be false. (Of course, interpretations of Scripture must also be consistent with Tradition in order to be accepted). The Bereans get praised for "receiving the word with all eagerness," not for accepting sola scriptura. But even if the Bereans got praised for checking their Scriptures to see if what the Apostles taught was in accord with their Bible, so what? Just because people are "searching the Scriptures" does not mean that Sola Scriptura is true.
Another argument goes: "If you want eternal life, what are you to search? The Bible says, ‘You search the Scriptures'" (John 5:39). Of course, this is not what the Bible means. Jesus is not saying that one should read the Bible because all Christian truth is found therein and every believer can discover that truth through his own private interpretation of the Scriptures. Jesus is not even commanding them to search the Scriptures in order to find salvation. He is describing what people were doing, and condemning their actions. He is saying that the Jews "search the Scriptures" without realizing that the Scriptures attest to Him and His claims.
Another passage goes as follows: "But these are written so that you may come to believe that Jesus is the Messiah, the Son of God, and that through believing you may have life in his name" (John 20:31). This verse means what it says-that the book was written as an evangelistic tool. It does not say the Bible contains all Christian truths.
"I have applied these things to myself and Apollos for your benefit, brothers, so that you may learn from us not to go beyond what is written, so that none of you will be inflated with pride in favor of one person over against another" (1 Cor. 4:6). "What is written," rather than being the Bible, refers to the Book of Life, where the names of the elect are written. Paul is commanding the believers not to have the attitude that "we are saved, and they are not–we are better than them."
Protestants say Jesus used the Bible to counter the arguments of Satan. Scripture alone was quoted. (Matthew 4:1-10 and Luke 4:1-12). In his debates with religious leaders, he also cited Scripture: "Did you never read in the Scriptures?" (Matt. 21:42; Matt. 22:29). But Jesus did not always appeal to Scripture. When he did, it was an appeal to the authority of Scripture, not to Scripture as the only authority. Jesus had yet to set up his infallible Magisterium, and the oral Tradition of the Apostles would be preached later. Jesus does not cite "Tradition" for the simple reason that His teaching itself was Christian Tradition. Catholics also agree with everything written in the Law and the prophets (Acts 24:14), but we do not take these writings alone as our sole authority.
The biggest problem with sola scriptura is the canon dilemma. Nowhere in the Bible does it say which books are inspired and which are not. Therefore, if the Bible must contain all religious truth, but the Bible does not tell us which books are inspired–which is a religious truth, then the Bible does not contain all religious truth and sola scriptura fails. The canon is not found in Scripture, and this contradicts sola scriptura, a doctrine which states that, regarding matters of faith, something must be found in Scripture in order to be believed. There is no way for Protestants to know which books belong in the Bible and which do not. After all, there were many other holy writings that the early Church councils prayerfully decided to omit from the canon. Who is to say these writings did not belong in the Bible?
If sola scriptura claims that all Christian truths must be found in Scripture, and if sola scriptura itslef is not found in Scripture, than the doctrine of sola scriptura refutes itself. The Catholic teaching, rather, is sola verbum Dei–the word of God alone, found in Scripture and Tradition.