On Pesach Night one of the most beautiful sections of the Seder is the Hallel. But for some strange reason we eat a meal in the middle of the Hallel. This Hallel is unique in that it is said not a a Tefillah but as a Shira that we all say.
Rabban Gamliel famously stated that if you don't mention Pesach, Matzah, and Maror during the Seder you aren't Yotzei. Why would these mitzvos have this added requirement? The ultimate message is to know that Hashem is the master of all nature and events and Geulah can arrive at any moment, no matter how dark it may seem.
There is a strong connection between Parshas Vayikra and Pesach. Learn the deeper meaning behind the prohibition of eating Chametz.