Musar על בבא בתרא 156:5

We learned (Bava Bathra 78b): R. Shmuel b. Nachmani said in the name of R. Yonathan (Bamidbar 21:27): "Therefore, the rulers say: 'Let us come to Cheshbon, etc.': 'the rulers' — these are the rulers over their yetzer. 'Let us come to Cheshbon' — Let us come and make the world's accounting ['cheshbon' = account], the loss [entailed by the performance] of a mitzvah against its reward; and the reward of a transgression against its loss." The plain meaning is well known: this [the reward of a mitzvah] is forever, and this [the "loss" of a mitzvah] is temporal. Also, this [the "reward" of a transgression] is a negligible pleasure, and this [the reward of a mitzvah] is awesome. For "one moment of pleasure in the world to come is greater than all the pleasures of this world," and the opposite for transgression.