Our Sages teach us that Mashiach has to come at a time when no-one imagines he will come. Why does it have to be like that? Why was Daniel told to obscure it until the end of times? Why is Olam Haba - the World to Come not spoken about explicitly in the Torah? Rav Moshe Shapira explains that the world to come is a dimension beyond the limitations of words. Its too lofty to be able to be described. Mashiach is the bridge that takes us from this world to this new dimension - Olam Haba. The concept of Mashiach is revealed because he will arrive into this revealed world, but the day and time has to be obscured because he is coming from Olam Haba to take us back there with him. We don't want to know the date because then we have limited his ability to take us to new dimensions and levels.