Offering a sacrifice to God requires meticulous precision, demanding that one respects clear boundaries of time and spiritual purity. By setting strict rules for the Passover offering, God establishes a profound separation between holiness and human pride, ensuring that worship is an act of free will rather than mindless habit or compulsion [שפתי כהן]. Furthermore, the insistence on removing leaven and consuming the offering within a single night was designed to deliberately uproot ancient pagan customs, which often incorporated leaven into their rituals and left offerings lingering until the next day [מלבי"ם].
The prohibition against preparing the Passover offering while leaven remains is absolute and sweeping. It applies not only to the individual performing the slaughter, but also to the priest sprinkling the blood on the altar, and to every single person registered for that specific offering. If any member of the group still possesses leaven, even hidden away in their home, the entire group violates this command [רש"י, מזרחי, ביאור יש"ר, חזקוני]. Because the act of slaughter and the sprinkling of blood are intertwined, the instruction is understood as a dual command: one must neither slaughter the animal nor sprinkle its blood as long as leaven exists [מזרחי, גור אריה, ביאור יש"ר]. Alternatively, the specific reference to the offering's blood serves as a unique title for the Passover sacrifice, evoking the memory of the Egyptian firstborns' fate and the protective blood placed on the Israelites' doorposts [הכתב והקבלה].
The specific reference to physical slaughter, an act that can be performed by any Israelite and not just a priest, indicates that the prohibition of leaven begins at midday on the eve of Passover, the earliest possible moment the slaughter can commence [הכתב והקבלה, תורה תמימה]. On a deeper level, the act of slaughtering represents the nullification of the ego and complete devotion to God, whereas leaven serves as a symbol of human pride and material independence. It is conceptually impossible to offer a genuine sacrifice to God in the Temple while simultaneously harboring pride and leaven at home [רש"ר הירש]. Moreover, since the lamb was worshipped as a deity in Egypt, sacrificing it to God elevates it to the highest level of holiness. Consequently, one must completely eradicate the impurity represented by leaven before engaging in such a profoundly sacred act [נחל קדומים].
The requirement to complete the ritual before morning establishes a firm temporal boundary, with morning defined specifically as the break of dawn [רש"י, שפתי חכמים]. Commentators offer various perspectives on what exactly cannot be left over. Some maintain that the prohibition focuses on the sacrificial fats that must be burned on the altar during the night [רש"י, גור אריה], while others suggest it refers to the meat itself, which must be fully consumed or burned [חזקוני, שטיינזלץ]. A more comprehensive approach applies the restriction equally to the meat, the fats, and the blood [רמב"ן, שד"ל, ביאור יש"ר]. Another distinct perspective suggests that the rule actually governs the supplementary festival offering brought alongside the Passover lamb, ensuring that the primary Passover meat is eaten only after one is already fully satisfied [העמק דבר].
A central rule emerges regarding the mechanics of the altar: while leaving sacrificial parts off the altar until dawn renders them invalid, if they are placed upon the altar before dawn breaks, they remain valid and can continue to burn into the day [רש"י, מזרחי]. This restriction against leaving offerings overnight is not exclusive to Passover; it serves as a foundational rule for the fats and limbs of all sacrifices [רש"י, מזרחי, משכיל לדוד]. Ultimately, the terminology used to describe the Passover festival reflects a historical and spiritual reality where the Festival of Passover and the Festival of Unleavened Bread merge into a single essence [קאסוטו]. It beautifully demonstrates that the family dining table, where the meat is eaten, and the altar, where the fats are consumed, are inextricably bound together in the service of God [רש"ר הירש].