The Torah gives strict instructions about Passover leftovers: "You shall not leave over anything of it until the morning, and what is left over of it until the morning, in fire shall you burn it" (Exodus 12:10). The phrase "until the morning" appears twice, and the Mekhilta wants to know why. If the first mention establishes the deadline, what does the repetition add?
The first interpretation is precise and practical. "Until the morning" does not mean until sunrise. It means until the rising of the morning star — the astronomical dawn that precedes the sun's appearance. This sets an earlier deadline than a casual reader might assume. The Passover lamb must be fully consumed before the first light touches the sky, not before the sun crests the horizon. The doubled phrase, in this reading, refines the definition of "morning" itself: the morning of morning, the earliest possible meaning of the word.
The second interpretation takes the text in a completely different direction. The repetition of "until morning" teaches that the burning of Passover leftovers does not happen on the morning of the fifteenth of Nissan — the day after the seder — but rather on the eve of the sixteenth. This means there is a full day's delay between the deadline for eating and the deadline for burning. The leftovers sit untouched throughout the first day of the festival before being destroyed.
Both readings demonstrate the Mekhilta's foundational assumption: no word in the Torah is redundant. When God says "morning" twice, He means two different things. The first "morning" governs eating. The second "morning" governs burning. One word, two laws, and the entire Passover timetable pivots on the repetition.