Hi Lily,
When the Israelites were held captive in Egypt by an oppressive Pharoah, God showed his anger by killing the firstborn in all of Egypt (Ex 11:1-7). However, the Israelites would be spared if they sacrified a lamb. And so they did, and Passover is a festival to commerate this deliverance (Ex 12:1-12).
It is interesting to note that later Jesus would be crucified during a Passover festival (Jn 19:14). This is why he is referred to as the Lamb of God; He saved us from something far worse than an oppressive Pharoah - He saved us from sin! (Jn 1:29)
When Jesus was crucified, the veil in the temple was found to be torn (Mt 27:50-52). Christians believe that God was trying to tell us that we no longer need a high priest to offer the sacrificial scapegoat behind the veil. But the Jews fixed the veil and continued with their rituals. (I think this is known as Yom Kipper.) This continued until 70 AD when the temple was destroyed in the failed Great Revolt against the Romans. (I think the lamb at Passover and the goat at Yom Kipper are different.)
Since then, I think the Jews have had difficulty in reconstructing the day without the pageantry associated with temple life.
Catholics nowadays refer to the modern Passover as “Good Friday”. (I think the Orthodox still refer to it as Passover.)