Sufficiency of the Bible
The Book of Mormon purports to be a volume of scripture in addition to the Bible; however, the Bible says that “all scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness: that the man of God may be perfect, throughly furnished unto all good works” (2 Timothy 3:16-17). If all the scripture we need is already given we have no need for additional scripture such as the Book of Mormon.
Paul’s statement to Timothy only speaks of the usefulness of scripture in general and does not limit the amount of scripture that God can or will give through authorized prophets. When scripture is given it can be used for many things. The scriptures Paul refers to are the ones Timothy had known since he was “a child” (2 Timothy 3:15), which can only mean the Old Testament, since the New Testament had not yet been compiled and some of its books had not yet been written. Similarly, the scriptures that the Bereans searched to compare with the teachings of Paul and Barnabas could only have been the Old Testament (Acts 17:11). If one interprets Paul’s statement to Timothy to mean that no additional scripture is neccessary or of value, logically one would also have to reject the entire New Testament, including Paul’s epistle to Timothy.