the unleavened bread we ate because we had had no time in fleeing egypt to make bread with leaven ; the bitter herbs we ate because our captivity had been bitter ; the lamb we ate because we were free now and could feast for the lord had saved us ; and it was the blood of the lamb on the lintels of the israelites that had caused the angel of death to pass over us when that angel had slain the firstborn of egypt because pharaoh would n't let us go .