The Mekhilta has established the punishment and warning for daytime Sabbath labor. But what about labor performed at night — during the evening hours of the Sabbath? The day-based verses address labor during the daytime. A separate source is needed for the evening.
"Those who profane it shall be put to death" provides the nighttime punishment. The word "profane" encompasses any violation of the Sabbath's sanctity, whether by day or by night. We now have the penalty for evening labor. But where is the nighttime warning?
(Exodus 20:10): "And the seventh day is Sabbath to the Lord your God." Rabbi Yossi bar Rabbi Yoshiyah asked: why does the Torah write "Sabbath" when it is obvious that the seventh day is the Sabbath? The seemingly unnecessary word exists to include the evening. "Sabbath" extends the prohibition to the entire twenty-four-hour period — night and day alike.
The Mekhilta has now constructed a complete framework. Daytime labor: prohibited by "you shall not perform any labor," punished by death. Nighttime labor: prohibited by the "extra" word "Sabbath" in the same verse, punished by "those who profane it shall be put to death." Every hour of the Sabbath — from Friday evening through Saturday night — is covered by both a warning and a penalty. No gap exists in the law's coverage.