The Torah promises prosperity for the Jewish People if they follow
"If you walk in My laws…" (26:3)
The purpose of this world is to be factory to produce a product called “Olam Haba” — the World-to-Come.
That is our only target, and the mitzvot our only passport.
However, you can read the Torah from cover to cover and you won’t find one specific promise about the reward for keeping the mitzvot in the next world. Promises of reward in this world abound. We are promised the rains in their time; the land will give its produce and the trees will bear fruit; there will be an abundance of food that we will eat to satiety. We will dwell securely in our Land. No one will walk down a dark street and be frightened. No one will worry about sending their children off on the bus in the morning. There will be abundance and peace.
Why is it that the Torah makes no open promises about the reward for keeping the mitzvot in the next world, but is replete with details of their reward in this existence?
All reward and punishment in this world is through hidden miracles. When a person eats a bacon-cheeseburger and dies prematurely, nobody knows that he died because he ate a bacon-cheeseburger. People die at his age even when they don’t eat bacon-cheeseburgers. They die younger.
A person gives tzedaka and becomes rich. You don’t see that he became rich because he gave tzedaka. There are plenty of rich people who don’t give tzedaka and yet become rich by receiving an inheritance or winning the sweepstake. The hidden miracle is that a person who wasn’t destined to become rich or wasn’t supposed to die young, but because he gave tzedaka or because he ate the bacon-cheeseburger,
That’s why the Torah speaks at great length about the outcome of the performance (or non-performance) of the mitzvot in this world. For it is truly miraculous that our actions should affect anything in this world, a world that, aside from these hidden miracles, is run by a system of mazal and nature.
However, as far as the next world is concerned, it’s obvious that our actions will have repercussions there. The Torah doesn’t need to stress the reward and punishment in that existence because it’s obvious that people who engage in spiritual pursuits and serve
- Source: Ramban on the Parsha and at the beginning of Parshat Va’era