Hebrews 1:1-2 says: "Long ago God spoke to our ancestors in many and various ways by the prophets, but in these last days he has spoken to us by a Son...." 1 Timothy 6:14 says, "{I charge you} to keep the commandment without spot or blame until the manifestation of the Lord Jesus Christ." On these two passages in particular, the Catholic Church argues that there is to be no further revelation. In the first, the point is that the voice of the Son speaks with the authority of the Father and may not therefore be gainsaid. In the second, the point is that inspired scripture tells believers to keep THIS faith until Jesus comes.

I do not know much about Mormonism, but this seems to argue against the possibility of further divine revelation. Rabidcow is correct to point out that the literary history of the Bible is confused, but from a theological point of view, I have to stand with the New Testament statements on this issue, rather than argue for an all-inclusive scriptural structure.

One final note: while I am a Catholic myself, the Church does not represent the entire spectrum of Christian views, so the idea that the Church has some sort of ultimate authority over these questions (as suggested by both above writeups) will generate a good deal of flak from non-Catholics.

To my good friend Taltos: It is an interesting Johannine passage, but we can assume this means that Jesus did a lot more stuff--healings, exorcisms, etc.--than is practical to record. This does not imply that there are additional teachings which were edited out for lack of space. Of course, it could very well imply this, but it seems odd to think that the author of Gos. John would have omitted anything really important. But from a Catholic point of view, even Jesus's mere acts contain teaching points, encouraging us to go out and do good works. So that's a whole lot of meaningless nonsense I just wrote.