THE FOUR LEVELS OF REWARD FOR MITZVAH OBSERVANCE ACCORDING TO RAMBAN (VAYIKRA 18:4)
According to Ramban, know that a person’s reward for the observance of the commandments is in accordance with his/her preparation for them:
A person who fulfills the commandments not for Hashem’s sake, but in order to receive a material reward in this world, will be rewarded in this world with longevity, riches, possessions, and honor. It is concerning this kind of observance of the laws of the Torah that it is said, "in her left hand are riches and honor," (Proverbs 3:16) which the Rabbis interpreted to mean:(Shabbat 63a) “to those who engage in the observance of the Torah not for its own sake, there are material riches and honor.”
Those who engage in the observance of the commandments so as to merit reward in the World to Come, people who serve Hashem out of fear of punishment and for reward in the next world, will be found worthy on account of their intention to be saved from the judgments that will come upon the wicked, and their souls shall abide in joyfulness in eternal life.
Those who engage in the observance of the commandments out of love of Hashem, as is right and proper, together with worldly occupation, similar to what is mentioned in the Torah in the section of Vayikra 26:5: “And your threshing shall reach unto the vintage.” They will merit good life in this world according to the usual nature of things, and life eternal, in the World to Come, their merits will still be complete before them since the reward they received in their lifetime will not reduce that which is to come to them, in the hereafter.
Those who completely abandon the concerns of this world and pay no attention to it, acting as if they themselves were not creatures of physical being, and all their thoughts and intentions are directed only to their Creator, just as was the case with Elijah, [these people] on account of their soul cleaving to the Glorious Name will live forever in body and soul, as is evidenced in Scripture concerning Elijah [2 Kings 2:11] and as the Midrashim speak of Hanoch [Bereshit 5:24] and of those belonging to the World to Come who will rise at the resurrection.
It is for this reason that on the subject of reward for observance of the commandments the verses speak [in different ways, such as]: “that your days may be long” [Shemot 20:12] “that you may live;” [Devarim 16:20] “and that you may prolong your days.” [Devarim 22:7] For these expressions include all kinds of life, each according to his due.