The Cannon of the New Testament: Why Can't We Add on to It?

One reason the Bible is so important for Christians is because it is our sole means of clearly knowing God, including his plans and ways. In this book alone (with over 40 authors from all walks of life and written over thousands of years), God speaks clearly and definitively into actual lives and historical events until he fulfills all prophecy through his Son, Jesus Christ. Only Jesus can and has fulfilled the hopes of all the other Scriptures, of all the other prophets, and of all the previous types in Scripture. To the true student of the Bible, it is utter amazing.

But how do we know Scripture/ authoritative revelation ended with the apostles? Is there any reason to reject what Muhammad said or what Joseph Smith said, for example? How about if a Christian suddenly "heard a voice from God". Should it become Scripture? Here are some clues that I laid out recently for a couple friends:

Hi Guys,

I was thinking more about our discussion on how Jesus has wrapped up/fulfilled Scripture. (Name) pointed out the verse at the end of the book of Revelation (Rev. 22:18), which I do think carries great weight in the discussion. Though this verse is mainly discussing the actual book of Revelation, it seems, especially considering the contents of the book, that it should be a verse that applies to all revelation in the future. The other main verse I thought was Hebrews 1:1-2.

Hebrews 1:1: Long ago, at many times and in many ways, God spoke to our fathers by the prophets,
Hebrews 1:2: but in these last days he has spoken to us by his Son, whom he appointed the heir of all things, through whom also he created the world.

The last days of authoritative prophecy/ Scripture is wrapped up by what Jesus Christ and his chosen apostles said and did - Those who were with Jesus personally and were called to give His message to the world (Matt. 28:18-20) and promised that they would recall what was said, by the Holy Spirit (John 14:26). Paul (as he mentioned himself) was one "abnormally born", having received a revelation personally from Jesus after he had already returned to heaven. We are not to trust Joseph Smith or any other one-person revelation (ie. Muhammad) because they do not fit in with Jesus being the summation of all of Scripture, and because they do not bear the weight of historical scrutiny. They are individuals who rely completely on their own private revelation. Paul, on the other hand, met with the other disciples and they gave him "the right hand of fellowship" (Gal. 2:9). If anyone doubted his revelations, there were self-checks built in by the writings and authority of the other apostles.

Jesus validates the entire O.T. as being the Word of God, (Mt. 23:35 & Luke 24:44). We have clear testimony throughout Scripture and through general acceptance to know what Scripture is and what it contains. (Ex. Paul reaffirms Peter and Peter reaffirms Paul's writing as "Scripture" -2 Peter 3:16) Anything outside of this becomes a heresy.

God wants us to have confidence in his Word, the Bible.