Musar על אבות 4:17

But the one who does not always remember the day of his death is similar in his own eyes to one who has extra time and calm (mitun) to reach his goal. (It appears to me that it is from the usage [in Avot 1:1], "be patient [matunim] in judgement." And in Berkhot 20a, [we read], matun [which can also mean two hundred] and matun is equal to four hundred zuz.) And our Rabbis, may their memory be blessed, said (Avot 4:17), "more precious is one hour in repentance and good deeds in this world, than all the life of the world to come; and more precious is one hour of the tranquility of the world to come, than all the life of this world."

[And, in truth, how much should we be ashamed! For if two good, useful business opportunities presented themselves to a man, so that if he took one he would have to leave the other, he would look with a sober eye to determine which is certain and which is uncertain. And how much more so [would he choose the first] if it [the second] is only a possibility of a possibility. He would also look with a sober eye to determine which is better and more useful and which lasts a longer time. For sometimes, even if one is better than the other, if the second lasts for a longer time, he will choose that. How much more so if it is intrinsically better than the other. But when it comes to choosing between the service of the L-rd and the affairs of the world, the yetzer entices us to abandon the service of the L-rd, which is better and more useful in itself than all the affairs of the world, as the tanna has said (Avoth 4:14): "Better one moment in the world to come, etc.", and it is also eternal, as opposed to all the affairs of this world, which is only as a passing shadow. And also, the eternal reward that comes from serving the Blessed L-rd is a certainty than which nothing is more certain — and the yetzer entices us to leave all this because of the possibility of a possibility of [benefit in] this world! And this is what we say in the confessional service [of Yom Kippur]: "We have turned away from Your mitzvoth and from Your goodly judgments, and it was not comparable to us." That is, the eternal good was not [even] comparable in our eyes to the transitory good of this world. The proof: We have rejected the certain before the uncertain! And one who wishes to be saved from the enticement of the yetzer hara will reflect constantly within himself and consider the greatness of the pleasure of the reward that the Holy One Blessed be He will give him for [the observance of] His mitzvoth. As the GRA has written, that it is for this reason that the Holy One Blessed be He has created the eternal world with all that is necessary for the reward for fulfillment of Torah and mitzvoth and did not give His reward in this world. For even if a man were given all of this world and its pleasures for one mitzvah it would not suffice for the pleasure he deserves for the mitzvah. And if a man reflects upon this, he certainly will not reject the certain, eternal good for the possibility of the possibility (of pleasure) in this world.]

Now it is known that of all the hope of a man, ennobled by the name "Israel," the primary hope is to merit life in the world to come, the greatest delight of all the delights of the world. As stated in Avoth 4:17: "Better one moment of pleasure in the world to come than all the life of this world." And it is also known what has been written in many sefarim, including the GRA, on (Mishlei 13:13): "He who cheapens a thing will be injured by it," viz.: When a man cheapens a mitzvah, he injures himself. For every thing in his organs receives its vital force from a mitzvah. For the 248 positive commandments correspond to the 248 organs of a man, as we find in the Midrash, so that there is thereafter found [(by the cheapening of a mitzvah)] an injury in the soul in [the area of] the corresponding limb.