Pesah - Current vs. First
There are several obligations mentioned for the Pesah [Passover], some of which
applied only to those in Misrayim [Egypt] and not to future generations, see: Shemot [Exodus] 12:3-11 and Shemot [Exodus] 12:22. Other
obligations applied both to them and to future generations, see Shemot [Exodus] 12:15, which implies the removal of all leaven
before the arrival of the time of the slaughtering of the paschal lamb, meaning
before the first part of the first day of the seven days of unleavened bread. This is similar, in its application to future generations, to the
ordinance, “You shall not cause fire to burn in any of your settlements on the day of Shabbat” (Shemot [Exodus] 35:3).