The Beis Aharon zt’l (p.93:) writes, “The six days [of Pesach] are a preparation for

the seventh day, for the primary day is the seventh day of Pesach, since that is

perfection, the day they said shirah.” Rebbe Mendel of Riminov zt’l said, “I

heard from a gadol, a student of Rebbe Elimelech of Lizensk zy’a, who repeated

in the name of his Rebbe that the time most mesugal for attaining emunah is the

night of Shevi’i shel Pesach.