Although there is spiritual reward in the World to Come, this reward is not mentioned explicitly in the Torah. However, reward in this world for the fulfillment of mitzvot is mentioned explicitly. There are several reasons why the Torah does not mention reward in the World to Come.

The Torah mentions only reward in this world but not reward in the World to Come:

His main point is to remove any criticism and complaint from our holy Torah by those who would say: “I have room to claim that since the reward for the soul is not mentioned in the Torah, [performing] these commandments certainly cannot give those who do so any spiritual reward in the World to Come. The goal of performing [mitzvot] is only to receive reward in this lowly world.”

According to the Rambam, material bounty makes possible the study of Torah and the fulfillment of its mitzvot. The true reward for mitzvot is not mentioned in the Torah, so that it does not become the motivation for keeping the mitzvot:

The Rambam’s approach is that the [worldly] rewards mentioned in the Torah for observance of the mitzvot are not the true reward. They are mentioned merely in order to indicate that when people fulfill mitzvot, God will remove all disturbances such as war, illness, famine, and other calamities, so that they can continue to serve God wholeheartedly and without distraction. However, the true, spiritual reward and punishment are not mentioned, so that people will serve God unconditionally and not in order to receive that reward or in order to avoid that punishment.

According to Ibn Ezra, spiritual reward is an abstract concept that is difficult for the simple masses to grasp:

The approach of Rav Avraham ibn Ezra is that it is difficult to imagine [the true] reward, because a physical being cannot grasp a spiritual concept. Therefore, the Torah hid that deep matter from the masses, because of their inability to understand it.

According to Rabbeinu Baĥya, the Torah focuses on physical reward because it is more miraculous than spiritual reward:

The approach of the venerable Rabbeinu Baĥya [ibn Pekuda]…is that all of the rewards that the Torah promises are supernatural, for it is not natural that rain should fall when people observe mitzvot, and be withheld from the earth when people do not act in accordance with the will of the Omnipresent, blessed be He. However, the fact that the life force returns to its source [through one’s mitzva observance] is a natural phenomenon for the soul, and is not miraculous.

According to Rav Yehuda Halevi and Rabbeinu Nisim, the Torah’s account of physical reward includes an allusion to the core of the spiritual reward: Cleaving to God:

Since it is stated: “I shall walk in your midst” (Leviticus 26:12), and “I will place My dwelling in your midst” (Leviticus 26:11), meaning that the Divine Presence will cling to Israel even in this world, where the soul is entwined with physicality, all the more so is it true that [the soul] will cling to the Divine Presence after it separates from physicality (after death). Everything the false religions promise after death the Torah promises us even in this worldly life, and [the fact that] prophecy exists in our midst proves this. This approach is also found in the response of the Sage to the king of the Khazars in the end of Section 1 of his book, and Rabbeinu Nisim takes this approach in his new [collection of] sermons.

According to Rav Yosef Albo and the Ramban, the Torah mentions the physical reward for mitzvot because it is common to all, and the Torah addresses everyone:

All of the rewards mentioned in the Torah are for the nation as a collective, for the world is judged according to the majority of the people, and the rewards of rain, produce, peace, and the like will come to all of Israel as one. But the reward of the soul in the World to Come is not given to the nation as a collective; rather, each person is judged individually according to his actions…. This approach appears in Sefer HaIkkarim and in [the writings of] Ramban. (Rabbi Shlomo Ephraim Luntschitz, Keli Yakar, Leviticus 26:12)

Further reading: For more on spiritual reward and punishment in the afterlife, see p. 165.