What precedent is there in the bible for a 'further revelation' of fundamental truths about Deity?

Future revelations/doctrine beyond Rev 22:18?

By that same logic Deut 4:2 (Deut 12:32) would discount Revelation and the whole New Testament. The LDS believe this verse is pertaining to the manuscript of John's not the bible or New Testament.

When John wrote the Book of Revelation in the latter part of the first century A.D., he was not writing the concluding pages of the New Testament, as there was no New Testament in existence at that time....Nor was his manuscript necessarily the last one written. It is the consensus of those who have written on the subject that several of these 27 scrolls were written after the Book of Revelation was written.¹

What support can be given from within the bible (Genesis to Revelation) of the 'further revelation' which is said to have occurred in 1829?

Apostasy

The LDS church believe a falling away would happen. Amos 8:11-13

11 ¶ Behold, the days come, saith the Lord God, that I will send a famine in the land, not a famine of bread, nor a thirst for water, but of hearing the words of the Lord:

12 And they shall wander from sea to sea, and from the north even to the east, they shall run to and fro to seek the word of the Lord, and shall not find it.

13 In that day shall the fair virgins and young men faint for thirst.

Amos 3:21

21 Whom the heaven must receive until the times of restitution of all things, which God hath spoken by the mouth of all his holy prophets since the world began.

Scriptures

The LDS believe the stick of Judah refers to the Bible, while the stick of Ephraim refers to the Book of Mormon.

Ezekiel 37:16-17

16 Moreover, thou son of man, take thee one stick, and write upon it, For Judah, and for the children of Israel his companions: then take another stick, and write upon it, For Joseph, the stick of Ephraim, and for all the house of Israel his companions:

17 And join them one to another into one stick; and they shall become one in thine hand.

Prophecies^{2 contains longer explanations}

Isaiah 11:1,10-12

• Stem of Jesse-Jesus Christ
• rod, root-Joseph Smith

Isaiah 29:11-12

• words of a book that is sealed-Book of Mormon
• one that is learned- Charles Anthon
• him that is not learned-Joseph Smith

Isaiah 40:3-5

• the voice of him that crieth-Joseph Smith

Jeremiah 30:17,21

Malachi 3:1-3

• messenger, forerunner-Covenants conveyed by Joseph Smith

Revelation 14:6-7

• another angel fly- Moroni, John the Baptist, Peter, James, John, Elias, Elijah, Moses, Michael, Gabriel, Raphael, divers angels who restored keys and priesthood authority

JST contains more references, but that would rely on first accepting that Joseph Smith was a prophet.

• Genesis 50:30-31,33
• John 1:19-25

Prophets

see below

What prepares me in the holy scriptures already provided over a period of two thousand years - and after another period of another two thousand years - for a fundamental, unprecedented 'revelation' which has been kept from humanity since the foundation of the world and has now been revealed to a single individual?

That is how the Lord works by revealing things previously unknown/unprecedented through his mouthpiece, a prophet. Amos 3:7

Surely the Lord God will do nothing, but he revealeth his secret unto his servants the prophets

This pattern can be seen throughout the bible (Moses, Isaiah, Jesus, Amos, etc). See also dispensations

Nevertheless, the validity of the divine calling of Joseph Smith rests not on ancient scriptural records, but on the appearance of God the Father and His Beloved Son, Jesus Christ, to the young Prophet in the spring of 1820.

...

Of that man, Elder Joseph Fielding Smith wrote, “If a person thinks the name of Joseph Smith ought to be found in the Bible spelled out in so many letters, he will search in vain.” (Answers to Gospel Questions, 3:6.) That is true; the Prophet Joseph’s name is not found—at least not in the King James Version. Nevertheless, if we search the scriptures with an eye of faith, we will discover that the Lord truly did foretell the coming of his great latter-day prophet, Joseph Smith.²

_{1 How do we explain Revelation 22:18?}

_{2 Prophecies in the Bible about Joseph Smith]}

_{All emphasis mine}

I am addressing this question as a broader spectrum question than LDS doctrine alone, under the thought that a broader answer was the intended desire.

The entire Bible stands as evidence that further revelation should be expected. Throughout its pages, we see angels, prophets, visions, and miracles both grand and small. Recounting each would be tiresome and, I think, meritless for our purposes.

How is this evidence that further revelation should be expected?

Malachi 3:6

For I am the Lord, I change not;

Hebrews 13:8

Jesus Christ the same yesterday, and to day, and for ever.

Psalm 102:25-27

Of old hast thou laid the foundation of the earth: and the heavens are the work of thy hands.

They shall perish, but thou shalt endure: yea, all of them shall wax old like a garment; as a vesture shalt thou change them, and they shall be changed:

But thou art the same, and thy years shall have no end.

If God doesn't change, why would He stop talking to individuals? Why would angels stop visiting individuals? If he called prophets and Apostles in times past, why not now?

Certainly, the Catholic Church believes this is the case, as a very cursory glance at The Holy See's website indicates Apostolic letters, exhortations, and constitutions. A perusal of Catholic history makes it clear that various popes had no hesitation in issuing both interpretations of existing scripture and also new revelations applicable to their times. Whether one individual or another agrees with anything said will, obviously, depend on the individual's beliefs, but there can be no doubt that the popes claimed to be receiving revelation from God.

Catholicism is hardly the only mainstream group to claim revelation from God. LDS doctrine holds that new prophets have been called, and just about every denomination I have interacted with agrees in receiving some form of personal revelation, though they usually do not canonize such instances in scripture.

The original question focuses much on scripture and whether we should have any more added to that found in the contemporary Bible. If a revelation from God to man is not scripture, then I'm not sure how to define the term. Whether all revelation should be in scripture is another matter; certainly, one could judge some statements to be of greater worth than others- I myself struggle with the Song of Solomon, despite its presence in the Bible itself!

We then arrive at the Antilegomena and other portions of scripture which various individuals claim are more or less valid than other portions. Martin Luther was one to have such questions, just to name a prominent individual we are all familiar with. Questioning whether all portions of the Bible are actually scripture, and debating which parts are, was not uncommon in centuries past. The Catholic Church did not settle the matter until after several ecumenical councils, with the current version set forth in 382 AD- well after the Apostles. The Catholic Bible does not even match the Bibles used by protestant groups today!

Ah, but of course we can say that all the books in the Bible were put forth before Christ or resultant of His direct teachings while on Earth, but this is also false. The Apostles demonstrate repeatedly that they received new information from God, such as Peter's vision concerning the gentiles (see Acts chapter 10).

But then one could argue it must come from an Apostle set forth by Christ during His earthly ministry. That brings us back to Acts, where in chapter 6 they pick seven others to assist them. One of those, Stephen, has his testimony and teachings in Acts, thus being scripture.

That gives the precedent for others chosen by Apostles to have something worth putting in scripture. This supports claims held by various churches, from Catholicism to some protestant groups, as well as restorationists like LDS, which claim some form of authority from Apostles, either through bishops past or angelic visitations, all or any of whom could have received revelation, and that revelation could be deemed important enough to be in scripture, given precedents set in the Bible itself.

One could argued that all of this is bogus, that only the Apostles and prior prophets could record scripture, and Stephen's words were approved of by Peter directly and thus included in scripture. Then such an individual would have to go back to the ecumenical councils and carefully consider what was and was not accepted into the Bible, since if one claims only the Apostles could judge what is scripture, then those attending the councils would not be qualified of making such determinations.

God Himself could certainly add to established scripture, and as we began the conversation, if God does not change, then we must accept at least the possibility that He might have more to say to the world at large. Another possible author becomes John. This is open to interpretation, but some take John 21:20-23 to indicate that one Apostle still walks the earth and could thus make qualified judgements of what is and is not scripture, and possibly add to it.

I am aware of many who have either claimed to be Christ or claimed to speak for Him or on His behalf. I see no reason given in the Bible to claim this is impossible, and every reason to say it is possible. Obviously not all who have those claims actually were correct, but determining which if any are/were is well beyond the scope of this question.

I can't say I'm familiar with anyone claiming to be John or speaking on his behalf, though I imagine there surely must have been someone doing so at some point.

To conclude, Biblical verses and patterns have set forth that God has spoken, that He doesn't change, and that He still can speak. Whether He has spoken since the New Testament, and if so, to whom, is another question. Whether any such words could be considered scripture seems like a semantic question, for if one accepts words as coming from God, then such words would have the same weight as scripture regardless of where the words themselves are recorded.

The entire New Testament is a precedent for the further revelation of fundamental truths about Deity. Some few Jews believed what Jesus said about Himself, and such explanations and expositions of Moses and all the prophets as He gave to disciples on the road to Emmaus (Luke 24:27), but more of them adhered to the traditions of the elders, particularly the Pharisees.