Moses gave the Israelites a simple instruction in (Exodus 16:19): do not leave any manna over until morning. What happened next exposed a fault line running through the entire nation.
The Mekhilta DeRabbi Yishmael identifies exactly who disobeyed. "They did not heed Moses" refers to the faithless in Israel, those who did not trust that God would send fresh manna the next morning. "And men left over of it" draws a sharp distinction: good men did not leave any over. Men who were not good did. The Torah does not call them wicked or evil. It simply says they were "not good," a precise and devastating understatement.
But the Mekhilta noticed something else, a problem in the text itself. (Exodus 16:20) says the leftover manna "raised worms and was rotted." The rabbis pointed out that this sequence is inverted. In nature, something rots first and then attracts worms. Worms do not appear in fresh food. The manna should have rotted and then raised worms, not the other way around.
The proof comes from (Exodus 16:24), which describes the Sabbath manna in proper order: "it did not rot and there was no worm in it." Here the Torah lists rotting first and worms second, confirming the natural sequence. The reversed order in verse 20 was deliberate. The Torah inverted the process to show that the punishment for hoarding the manna was itself unnatural. God made the manna spoil in an impossible way, worms before rot, to signal that disobeying Moses carried consequences that defied the ordinary course of nature.