The gemara discusses whether we assume that there is a concept of מיתה בלא חטא and suffering without sin. Tosafos explains that אין מיתה בלא חטא means that Hashem can punish even for accidental violation. In other words, if we are to hold that there must be sin associated with death, that means that the bar of what is considered a sin has to be low to include even accidental violation. The gemara ultimately proves from a Braisa which says that there were 4 people (Amram - father of Moshe, Binyomin - son of Yaacov, Yishai - father of Dovid, Kela'eiv - son of Dovid) who died בעטיו של נחש, only because of the original sin committed by chava without having a sin of their own, that there can be death without sin. Therefore the gemara concludes - יש מיתה בלא חטא ויש יסורין בלא עון. Tosafos points out that even though we only prove the first part - יש מיתה בלא חטא, once we prove אין מיתה בלא חטא is wrong, we also assume אין יסורין בלא עון is also wrong.
This gemara seems to undermine the entire concept of reward and punishment. How are we to believe that one can be punished without doing any aveiros? Although Tosafos in Brachos 46b seems to take this more literally that there can be death and punishment without sin, the Meiri here has a different approach. The Meiri understands that the concept of reward for mitzvos and punishment for aveiros if מעיקרי הדת, a fundamental principal of our belief. Therefore, we definitely assume that there cannot be death or punishment without sin. Nevertheless, we consider these 4 people to have died only because of the sin of chava as a way of exaggerating their purity and minimizing the possible aveiros they may have committed. The bottom line according to the Meiri is that everyone must have sinned at some point and no one will ever be killed just for the sin of chava.