Talmud Pesachim 56a teaches us that Yaakov wished to reveal to his sons the end of the withdrawal of G - d's right hand from battle against the enemies of the Jewish people but the Shechinah (G - d's presence) departed and thus his ability of prophecy came to an end.
G - d's withdrawal of His right hand means metaphorically speaking "withdrawing His power and letting the enemies succeed over Israel". See, for instance, Nebuchadnezzar or the Romans.
While reading this Gemara, I started asking myself what would have happened if Yaakov had told all prophecies concerning the Jewish people ? Lets say he had told his sons and two grandsons (Menashe and Ephraim) about the Ge'ulah (Redemption) and when it is supposed to come along. Lets assume he would have foretold all the sufferings in exile, the pogroms the kings in Israel. Would the Jews then sinned and basically caused their own Galut (Diaspora) ?
Maybe not but what we always learn is that G - d created this world for us humans with the concept of "Free Will - Bechirat Chofshit". And now imagine where our free will would have been if Yaakov had announced all these events which are going to happen. It is very human for us not to behave properly, rebel and in the end cause exactly all those punishments like the Galut. Loosing the country, the Beit HaMikdash, doing Teshuva and hoping for a positive change.
Already the prophets had foretold the destruction of the Temples but no one wanted to listen. In a way, the Jews then used their own free will. However, being foretold the exact arrival date of Meshiach would cause a different reaction. After the destruction of Beit Sheni (Second Temple) the Jews were very much aware of the fact that Meshiach will be coming one day but until then, we have to do something in order to cause the arrival. Tikunim (soul rectifications by Mitzvot etc.). Would the Jews have done so if they knew the exact date of Meshiach's arrival ?