Frequently psalmists asked God how long before He would save them, or for how long would He seemingly stay hidden. Some people in heaven asked the same question after they had been killed on the earth,

“And they cried with a loud voice, saying, ‘How long, O Lord, holy and true, until You judge and avenge our blood on those who dwell on the earth?’” (Revelation 6:10).

In my judgment, the rest of the Book of Revelation answers that question. If you can read Revelation with that question in mind, it will help you to see why God gave us the Book of Revelation.