“Ya’akov Avinu wanted to be megaleh (to reveal) ‘the keitz’ (the time of Moshiach’s coming, and the end of golus [period of hiddeness before the coming of Moshiach]) to his sons. But HaShem did not want him to do so; and blocked Ya’kov Avinu’s access to the necessary information.
The Sfas Emes quotes… the Chidushei HaRim — who, in turn, quoted the Rav of Parshischa…who asked a basic question: What good would it have done to Ya’akov Avinu’s descendants if he had revealed the keitz to them?
…In standard usage, the phrase ‘to be megaleh the keitz’ means: to reveal when Moshiach will come and the golus will end. By contrast, the Sfas Emes and his illustrious predecessors read this phrase as meaning: to reveal the fact that a keitz exists.
…Knowing that the golus will end makes it easy to experience the whole golus period — regardless of how long it will last and when it will end. Indeed, says the Sfas Emes, if the fact of the keitz had been revealed, ‘lo haya golus klal’ (it would not even have been golus.)
Knowing that there is a keitz will give meaning to history, removing the impression that history is nothing but a sequence of random , painful events. Thus, knowing that there is a keitz would make it readily apparent that what we have been experiencing is only Hester, behind which HaShem is truly there.”