How long was the book of Daniel to be sealed until the time of the end?

From Daniel's perspective around 500 B.C., the book was to be sealed until the time of the end, a span of about 2,500 years. God instructed Daniel to shut up the words and seal the book, meaning it would stay closed and not be considered much until the end time.

Les teaches that God told Daniel to shut up the words and seal the book even till the time of the end. From Daniel's perspective around 500 B.C., that span would be about 2,500 years during which the book would be closed up and not considered all that much. At the time of the end, many shall run to and fro and knowledge shall be increased. The sealing does not mean the book is unimportant, but that its full understanding awaits the end times.

Daniel 12:4

But thou, O Daniel, shut up the words, and seal the book, even to the time of the end: many shall run to and fro, and knowledge shall be increased.

Why was the book of Daniel a closed book to scholars and theologians throughout history?

Daniel was sealed until the time of the end. Because it contains extensive end-time prophecy, most scholars and theologians throughout history could not comprehend it, so it remained a closed book. Scripture says it would be opened at the end time, which is now being witnessed.