Revelation 22:10

10 And he saith unto me, Seal not the sayings of the prophecy of this book: for the time is at hand.

Again, we are told this book is a prophecy. John is told not to seal it because the future things written in it started with the letters to the seven churches in Asia. Some of these things written to the seven churches actually did begin in John's lifetime. Daniel's prophecies tell about this period and more but it is a sealed book. It is sealed, because Daniel's prophecy is primarily about Israel and how the Gentile nations interact with Israel. Up until now, Israel has been in darkness and she will not receive light to unseal the prophecies of Daniel until she finds herself in the middle of the prophecies of that book in the last days.

The book of Revelation is written to those who are in spiritual light. The passages for those in the light cannot be sealed. The book is only sealed to those who live in spiritual darkness. Those in Christianity who say Revelation is a sealed book or that it cannot be understood are in darkness. The seven thunders are sealed in this book but the thunders are just prior to God's wrath and therefore the Church and Satan has no need to know what they announce.