The Fourteenth of Nissan
The fourteenth day of Nissan, is different from all of the days of the year. During daylight hours, we begin the day being permitted to eat foods that are not kosher for Pesach, but by midday, we have a Torah prohibition from eating such food.
The Rabbis added additional time as a precaution. If it was a cloudy day, before clocks existed, there could be confusion as to when noon would appear. This is why the last hour for eating Chametz, is two hours before noon.
This is learned from the verse, אך ביום הראשון תשביתו, “But on the first day, you shall remove.” The additional word, אך, is teaching אך חלק, that the word, אך, is coming to divided the day.
This day was technically called, “Pesach,” as it was the day that the Korban Pesach was slaughtered and prepared for the Seder. Some of it was offered on the altar, and the rest was eaten at the Seder.
As the day progressed, more prohibitions kick in, as the transition is made from the profane, to the holy days of Passover. Eating Chametz in the afternoon, is punishable by lashes. But eating after sundown, is a Karet penalty.
It is one of the more amazing logistical problems, that was solved on Erev Pesach on the fourteenth. All of Israel needed to make the pilgrimage to Jerusalem for Pesach. And everyone needed to eat from the meat of the Pesach sacrifice. This meant that an incredible number of lambs were offered as sacrifices on that day.
The Temple staff needed to be extremely organized to handle that amount of people with their sacrifices. Somehow they figured out how to do it.
The fourteenth of Nissan was truly different from all the days of the year.