And he said, Go thy way, Daniel; for these words are "closed and sealed" till the time of the end.
The Hebrew Bible uses the verb חָתַם in two ways.
The first is the common use of seal as royal cachet. The idea here is that the king's edict is irreversible. Thus Jezebel (1 Ki 21:8) and Mordecai (Esther 8:8) seal the royal decrees as mandates "ex officio" from the king. The seal was therefore the explicit authority of the king.
The second and related use is therefore to prevent something from leaking. Thus in Lev 15:3 the same Hebrew verb is used to indicate blockage of bodily fluids -- that is, Moses wrote that certain human anatomy prevented the discharge of certain unclean bodily fluids. (Think of the seal on the engine block of your car that prevents the leakage of oil.) In this same light, Isaiah 29:11 indicates how the contents of a scroll are prevented from spilling out and therefore being revealed. (Thus is Jer 32:11-14 an unsealed scroll, which was readable, had to be paired with the duplicate sealed scroll that was the original deed of transfer for real estate, which could not "leak" information.) In fact, the Hebrew verb חָתַם occurs four times in the Book of Job and has the EXCLUSIVE meaning of the prevention of disclosure (i.e., Job 9:7 from disclosure or appearance of light by the sun and stars in night and day, respectively; Job 14:17 from disclosure or appearance of guilt; Job 24:16 from disclosure or appearance of the sinner in the daytime; and Job 33:16 from disclosure or appearance of foolishness). In other words, the Hebrew Bible idea of sealing not only included the sacrosanct and irreversible nature of written royal decrees, but also included the idea of keeping something safe from leakage or disclosure. Think of a sealed grand jury subpoena or the oil seal on the engine block on your car to use modern examples.
So what we therefore see in Daniel is the secondary nuance of the Hebrew verb. That is, the verb occurs four times: Dan 9:24 (twice); Dan 12:4; and Dan 12:9. In each of these verses the emphasis is on the secondary meaning of the Hebrew verb: thus in each of these verses we find that divine revelation is checked from escaping and leaking out (because it is sealed). It is not until we arrive at the Book of "Revelation" that the Lamb appears with the key of David (Rev 3:7), and he therefore is the one who unlocks or breaks the seals of this scroll so that they unfold and "leak out" (Rev 5:1-14). It is not that he compromises the sacrosanct nature of the Word of God by breaking the seals (which is NOT the meaning here), but that by breaking the seals he allows divine revelation to leak out and therefore to bring to full disclosure ("revelation") what is to occur in the end times (which is the explicit purpose mentioned in Rev 1:1). Of interest, the content of Dan 11 and Rev 5 are parallel in content, and thus lend credence to the proposition that the scroll that appears early in the Book of Revelation is, in fact, Daniel's scroll.
The book of Daniel is an early example of the apocalyptic genre, which includes the book of Revelation in the New Testament, and several apocryphal books. Books in this genre, though written over the span of several centuries, carried many similar features, including:
For comparison, 1 Enoch (which was written/edited around the same time as Daniel) opens with the statement that the prophecy 'is not for this generation, but I speak about one that is distant' (1.2). The Assumption of Moses has Moses instructing his listeners to put his prophecies into jars and hide them away until 'the day of repentance' during 'the consummation of the end of the days' (1.16–18). Two other examples can be found in 2 Esdras 12.35-38 and 14.1-9. In Daniel, the prophet is told to seal his prophecy because 'it refers to many days from now' (8.26), and shall be sealed 'until the time of the end' (12.4,9).1
The reason for this 'sealing' of such prophecies comes down to the nature of the apocalyptic genre. Apocalypses are written in response to events contemporary with the author. In order to address those events under the mantle of prophetic authority, the author writes under the name of an ancient figure from the Hebrew scriptures (known examples include Abraham, Jacob, Moses, Elijah, Ezra, and Baruch).
But despite having given his prophecies a degree of credibility, this might cause people to wonder why such a famous biblical figure's prophecies have only just recently been discovered. The answer: they were hidden away, with the instruction that they were to be found again during the precise time that the prophecies are concerned with.
On the apocalyptic genre in general, Schneemelcher writes, 'it has to be made clear why the book has just recently become known and not a long time ago', and this is explained by 'the command for its secret preservation till the end of days'.2
On Daniel in particular, Collins writes, 'The command of the angel in Dan 12:4 to "shut up the words and seal the book" must be regarded as a consequence of pseudonymity - it explains why the revelations of Daniel had not been circulated before the Maccabean era.'3
1 One notable exception is Revelation 22.10, where the author is specifically instructed to not seal up his prophecies 'because the time is near'.
2 Wilhelm Schneemelcher. New Testament Apocrypha: Volume Two, p 545.
3 John J. Collins. The Apocalyptic Imagination, p 112.