From Kingdom of Cohanim by Rabbi Avigdor Miller
“If you shall walk in my statutes” (Vayikra 26:3).
It is noteworthy that all the rewards for compliance with the Torah are solely in this life. Rambam (Teshuvah 9:1) explains that the promises for happiness in this life are not intended as the ultimate reward, but are promises of opportunity to accomplish more good deeds and to gain more merit.
The failure to utilize good health and tranquility is the greatest of misfortunes
Similarly, the retribution of unhappiness which is foretold for transgression of virtue is not the ultimate punishment, which is in the Afterlife; but Hashem foretells the loss of opportunity to accomplish righteous deeds due to various forms of suffering. Thus it is said: "The reward for a mitzvah is a mitzvah, and the reward for a transgression is (another) transgression" (Avos 4:2), because he who seeks to do mitzvos is rewarded with opportunity to do more; and this is the greatest of rewards, as is said: ״Better one moment of Torah and good deeds in this world more than all the life of the World to Come" (ibid. 4:17).
Peace and prosperity are therefore to be very greatly prized, and must be utilized for their great opportunity to achieve; for this gift of opportunity is the greatest of gifts. We also learn therefrom that the failure to utilize good health and tranquility is the greatest of misfortunes, worse than famine and war and pestilence.