פת במלח תאכל - לא על העשיר הוא אומר שיעמוד בחיי צער כדי ללמוד תורה, אלא ה"ק אפילו אין לאדם אלא פת במלח וכו' ואין לו כר וכסת לישן, אלא על הארץ, אל ימנע מלעסוק בה, דסופו ללמוד אותה מעושר׃
Rashi's commentary (Rough translation):
"This is not speaking of the wealthy person who will suffer in order to learn Torah. Rather, what it means is that even if a person is eating bread and salt, etc. (as in the rest of the quote left out in the question), and he doesn't have a cushion (pillow/mattress) and blanket to sleep, but [must sleep] on the earth, he must not stop busying himself with [learning Torah], that in the end he will learn it [as a] wealthy [person]."
So, first of all, it's not talking about keeping the Torah (Mitzvoth), and it is not saying you will suffer as a result. It's talking about learning Torah, and it is saying you have to give of yourself to study, no matter the cost, even if you have nothing.
Also, the question asks specifically about the Mishnah in Avoth (6:4), but this takes the quote out of context. A reading of the entire chapter in Avoth should leave a person with the conclusion that RIBa"L feels, like R' Meir, that learning Torah is so vital to survival that one must even when faced with adversity, and that he will be rewarded.