Every year Jews celebrate Pesach by preparing a meal of lamb, unleavened bread, and bitter herbs—symbols of that first miraculous Passover. The meaning of the lamb is obvious—it is about the Lamb of God, the Messiah, who would come to free us from death and the bondage of sin. Because the Israelites left in haste there was no time for bread to rise, thus the unleavened bread which is also a symbol of not being puffed up with sin. And the bitter herbs were to remind them of the long bitter years they were enslaved in Egypt.
Thus if the birth did occur during Passover, on that first Christmas night families throughout the land may have prepared and eaten their the bitter herbs, while the Son of God came into the world to offer a sacrifice that would set right all the bitter experiences of life. They may have eaten unleavened bread while the Messiah was born to save us from sin, and they may have tasted the Passover lamb, at the very moment The Lamb of God was being born.
Whether the first Christmas occured during Passover or not,the symbolism is beautiful. Because He was born, the nullifying effects of death will pass over all of us. He was born to save us, and we will live because He died.