Charles Ellicott 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)

Roast with fire. —Roasting is the simplest, the easiest, and the most primitive method of cooking meat. It was also the only method available to all the Hebrews, since the majority would not possess cauldrons large enough to hold an entire lamb. Furthermore, this requirement set this sacrifice apart from other victims, which were generally cut up and boiled (1 Samuel 2:14–15).

Unleavened bread ... bitter herbs. —Just as partaking of the lamb typified feeding on Christ, so the putting away of leaven and eating unleavened bread signified the putting away of all defilement and corruption before we approach Christ to feed on Him (1 Corinthians 5:8). As for the bitter herbs, they probably represented “self-denial” or “repentance”—fitting accompaniments of the holy feast, where the Lamb of God is our food. At any rate, they were a protest against that animalism which turns a sacred banquet into a means of gratifying the appetite (1 Corinthians 11:20–22).