Albert Barnes Commentary Exodus 12:8

"And they shall eat the flesh in that night, roast with fire, and unleavened bread; with bitter herbs they shall eat it." — Exodus 12:8 (ASV)

In that night - The night is thus clearly distinguished from the evening when the lamb was slain. It was slain before sunset, on the 14th, and eaten after sunset, the beginning of the 15th.

With fire - Among various reasons given for this command, the most probable and satisfactory seems to be the special sanctity attached to fire from the first institution of sacrifice .

And unleavened bread - Because of the hasty departure, allowing no time for the process of leavening; but the meaning discerned by Paul (1 Corinthians 5:7–8), and recognized by the Church in all ages, was certainly implied, though not expressly declared in the original institution. Compare our Lord’s words (Matthew 16:6, Matthew 16:12) regarding the symbolism of leaven.

Bitter herbs - The word occurs only here and in Numbers 9:11, in reference to herbs. The symbolic reference to the previous sufferings of the Israelites is generally admitted.