Musar su Deuteronomio 8:19

את הברכה אשר תשמעו . We may ask why the Torah (11,27) uses the preposition אשר when describing the blessing, whereas in connection with the curse the Torah (28,15) uses the preposition אם. Some commentators explain that we can understand this when we understand the saying of our sages in Avot 4,2 that שכר מצוה מצוה, "the reward of performing one מצוה is another מצוה" The meaning would be that "once you start listening to G–d's commandments your reward will be that you will feel the urge to observe still more of the commandments." This would be analogous to והיה אם שמוע-תשמעו, (11,13 et al). The difficulty with this explanation is that we find a similar construction used in the Torah when the opposite attitude is described, i.e. והיה אם שכח תשכח (8,19).