Rewards are relative, in the sense that what might serve as a reward for one person might not do at all for another. To an illiterate, a set of encyclopedias would be a burden, not a reward. What makes a response a reward is that it speaks to something in the individual’s horizon of actual desire. “My kingdom for a horse!” dramatizes this elemental human truth, as does “Hunger makes the best sauce,” and, in a different way, “Necessity is the mother of invention.” Worldly rewards are, so to say, parasitic on worldly desires.
Heavenly rewards have the same relationship to heavenly desires, but it is extremely important that we not do not confuse the vectors, and imagine heavenly rewards being parasitic on worldly desires. This way of thinking leads to the demonic picture of heaven as a harem filled with virgins.
The truth is that before anything available in heaven could be experienced as a reward, our desires must first conform to heavenly desires.
In the Talents parable, Jesus teaches that the heavenly reward for doing well is the opportunity to do better. In the Sermon on the Mount, He teaches that doing well in secret is something heaven rewards. Combine those two teachings, and we learn that one heavenly reward is ever deepening anonymity in charity.
Wouldn’t most of us, as presently constituted, find that about as rewarding as an illiterate receiving a set of encyclopedias?