According to the beginning of the Mesilas Yesharim, the entire purpose of creation is for man to merit Olam Haba (the bliss of the next world).
If so, why is there no mention nor description of Olam Haba in the Torah, except in vague shrouded terms?
(excerpt from Mesilas Yesharim chapter 1: Our Sages of blessed memory have taught us that man was created for the sole purpose of rejoicing in God and deriving pleasure from the splendor of His Presence; for this is true joy and the greatest pleasure that can be found. The place where this joy may truly be derived is the World to Come, which was expressly created to provide for it; but the path to the object of our desires is this world, as our Sages of blessed memory have said (Avorh 4:21), "This world is like a corridor to the World to Come." )
Furthermore, the Mesilas Yesharim starts off saying the foundation of religious service is to clarify for oneself what is his duty in this world and to what one should put his aspirations toward. This aspiration he says is to merit closeness to God in the Olam Haba. So it seems knowledge of Olam Haba is the foundation of the entire religious service in this world.