Have you ever wondered why Easter is not on the same date every year like Christmas? The reason is quite simple, it coincides with the Jewish festival of Passover whose date is determined by moon cycles. The rule is that it is on the first Sunday after the first full moon after the spring equinox (March 21st). This means that Easter Sunday can be on any date from 22nd March until 25th April. This year it is on 1st April and in 2019 it will be on 21st April. You will have to wait for 2038 before it falls on 25th April and until 2285 before it falls on the 22nd March!
What then is the connection between Easter and Passover?
Historically the first Easter weekend fell on the Jewish Passover. Jesus and his disciples were eating the Passover meal in the upper room when he instituted what we call communion. The legs of the two crucified next to Jesus were broken so that they died more quickly and their bodies could be removed from the crosses quickly before the Sabbath which was special due to the Passover.
Theologically the Passover celebrates the escape from Egypt by the Israelites under the leadership of Moses. Blood from lambs eaten at the first Passover meal were daubed on the door frames as a sign of protection from the angel of death who passed through the land killing the first born male in every family across Egypt, including Pharaoh. Those who acted in faith, and painted blood on their doorframes were passed over and their firstborn sons were saved. This desolation across Egypt finally caused Pharaoh to relent, and he allowed the Israelite people to leave the land. God instructed Moses to command that the Passover meal be eaten every year to remind them of how they had been saved.
Jesus took this powerful and yet familiar ritual and gave it fresh significance and poignancy. At the point in the meal when bread would be broken and shared together Jesus told his disciples that it now represented his body which hours later would be nailed to a cross for them. Similarly at the point in the meal when everyone would drink wine from the same cup he took it and told them that it was the new covenant of his blood which provides for the forgiveness of sin. Rather than an annual memorial he commanded them to remember his death whenever they ate bread or drank wine together.
The parallel is clear. Jesus was physically killed just like the Passover lamb, indeed Paul writing in 1 Corinthians calls Jesus our Passover Lamb. Jesus' blood was spilled over the cross akin to the daubing of blood on the door frames. That blood rescues us from the judgement of death just as the Israelites were saved from the angel of death.
On Easter Day itself we rightly celebrate Christ's resurrection and victory over death. But without the crucifixion there would be no resurrection and without the shedding of Jesus blood as our Passover lamb there would be no forgiveness of sin.