Daniel was a "closed" book until the coming of Christ. But since Christ said WHOSO READETH LET HIM UNDERSTAND in connection with Daniel, we are expected to understand what Daniel revealed in view of the NT prophecies, particularly the book of Revelation.
When ye therefore shall see the abomination of desolation, spoken of by Daniel the prophet, stand in the holy place, (whoso readeth, let him understand)...
Daniel already wrote history in advance (until the Roman Empire), but he also provided an insight into the future, which is Daniel's 70th week (the worldwide reign of the Antichrist and its aftermath).