Many Christians believe that the Bible is the only source concerning Truth since it contains all the Truth that Christians need to know. As a result, there is no modern need for prophets and apostles. The term “sola Scriptura” or “the Bible alone” is often used to explain that there is only one special revelation from God that man possesses today, the written Scriptures or the Bible.
However, the Bible would not be possible with out prophets to write down what God revealed to humanity. Prophets are the medium by which Truth is given to mankind. (Numbers 12:6, Deuteronomy 18:15, Deuteronomy 18:18, 2 Kings 21:10, 2 Kings 24:1-3, 1 Chronicles 29:29, 2 Chronicles 13:22, 2 Chronicles 18:6, 2 Chronicles 24:19, 2 Chronicles 26:22, 2 Chronicles 32:32, 2 Samuel 24:11, Ezra 5:1, Hosea 12:10, Zechariah 1:6, Amos 3:7, Haggai 2:1, Haggai 2:10, Jeremiah 35:15, Jeremiah 37:6, Jeremiah 45:1, Jeremiah 47:1, Jeremiah 49:34, Jeremiah 50:1, Matthew 23:34, Acts 3:22, Ephesians 3:5, Hebrews 1:1, 1 Nephi 19:4, 1 Nephi 22:2, Jacob 5:2, Helaman 13:26, D&C 21:1, D&C 107:92, D&C 124:94, D&C 124:125, and D&C 138:53).
As one studies the scripture, it is evident that God has a long-established pattern of calling prophets. Many well-known figures in the Bible, like Noah, Abraham, Moses, and others, were prophets. These men were chosen by God and given authority to lead His people. However, when people chose to ignore God, God took prophets away and waited until the people were ready to listen again. Thus, from the beginning of time emerges a pattern of prophets teaching the people, the people eventually turning away from God (a state called apostasy), and God sending prophets again to show His love and concern for His children.
Prophets have always been essential to God's method of sharing His knowledge to mankind as shown throughout the scriptures. God provided prophets to create scripture, and at the same time teach them what had been revealed before, since God's followers did not have access to the scriptures because it would not be "completed" until much later. Thus, the God sent prophets to proclaim His Word to His people to educate those who did not have His Word. Prophets are essential to the religion as established by God. (1 Corinthians 12:28, Ephesians 2:20, Ephesians 4:11, Revelation 11:10, D&C 124:125).
The Bible (and other scriptures) contain Truth but are not the source of Truth. The source of Turth comes from God Himself, who reveals Truth to his prophets and these prophets writes down what has been revealed to them. (2 Timothy 3:16–17, 2 Peter 1:20-21).
The Old Testament clearly demonstrates that God Himself is the source of Truth and that prophets are the conduit by which Truth is revealed to humanity. For example, King Jehoiakim had attempted to destroy God's Word by burning a roll written by Jeremiah. Yet, the Lord instructed Jeremiah take a new scroll and rewrite the words that were destroyed. (See Jeremiah 36: 27-28). However, not only did God have Jeremiah restore what was destroyed, but the Lord told him there were additional information (revelation) to write about on top of what was previously written before the King burned the roll.
This concept is also illustrated in the New Testament as well. For example, the Paul recived a revelation that the gospel should be taught to the Gentiles and not just the Jews. (Acts 10:1-48; 11:1-18). This revelation was then recorded as evidence that God still uses prophets to guide His people, even after Christ's death.
We also see this concept throughout the Book of Mormon. God gives specific instructions to His Prophets on what to write down and/or what not to write down. (see 2 Ne.4: 15, 2 Ne. 29: 11-12, 3 Ne. 27: 23-24 and 3 Ne. 28: 25).
The above scriptural examples from the Old Testament, New Testament and the Book of Mormon repeatedly show that the Bible itself is not the sole source of Truth. God is the source and inspiration of the scriptures and that the scriptures would not be possible without the prophets. There's no evidence that God shut the heavens and intended for mankind to only have the Bible. God frequently speaks to mankind via prophets thoughout history as evidenced by the scriptures and continues to do so today.
There are some Christans who have argued that the closing verses in the Book of Revelation, (specifically Rev. 22:18-19) cap off the Bible and define all the preceding Books as inspired by God. That is not possible because the Book of Deuteronomy contains similar verses (4:2 & 12:32). The only logical conclusion that the reader of the Bible can make is that God frequently revealed His Word to his Prophets throughout the Old and New Testament and that He continued to reveal Truth to people in other parts of the globe such as to those prophets in the Book of Mormon. God continues to provide revelation to His Prophets even today.
Another argument that some Christians make in defense of "Sola scriptura" is that there were to be no prophets after Christ. While, prophets are frequently found in the Old Testament, they are frequently found in the New Testament. Prophets existed in Christ's day. The New Testament shows that there was a prevailing belief in prophets before and during Christ's ministry. (Luke 7:16, Luke 7:28, Mark 6:4, Luke 11:29, John 4:19, John 4:44, John 6:14). The New Testament shows that prophets continued after Christ's death and will continue until Christ returns again a second time. (Acts 11:27, Acts 13:1, Acts 15:32, Acts 21:10 and Revelation 11:10.)
Another piece of evidence for prophets continuing after Christ's death is that Jesus warned that there would be many false prophets that would come after his death and that the followers of Christ should learn to discren who is a true prophet and who is not. (Matthew 7:15, Matthew 24:11, Matthew 24:24, Mark 13:22, 2 Peter 2:1, 1 John 4:1). Interestingly enough, God warned about false prophets in the Old Testament too. (Deuteronomy 13:5, Jeremiah 14:14-15, Jeremiah 23:21, Jeremiah 27:14, Ezekiel 13:3, and Matthew 7:15.) The Book of Mormon has a similar warning about false prophets as well. (Helaman 13:27). It is clear that separating the true prophets from the false prophets have always been a problem in the Old and New Testament, as well as the Book of Mormon, and that it would continue into the future until Christ returns again. The important lesson here is that scriptures are clear in showing that God is the source of Truth and He will verify who are His true prophets. These true prophets are authorized to share what He has revealed for all of mankind.
The scriptures consistently teach that God is the source of Truth, the Prophets are the medium by which God reveals Truth to mankind, and that the scriptures (the Bible, the Book of Mormon, the Doctrine and Covenants, and the Pearl of Great Price) are a record of the Truth that God gave to his prophets.
God still speaks His Truth to us today through His Prophets and his message is currently being recorded, preserved and shared in multiple mediums such as books, magazines, media and the Internet.