The Passover lamb, as directed by God in Exodus chapter 12, was to be "without blemish." Given by God as part of the flock of sheep tended by each shepherd, the chosen lamb was to be sacrificed following specific procedures. The blood of the lamb was to be painted on the doorposts and lintels of the houses in which the people gathered to eat the sacrificial lamb.
The blood shall be a sign for you, upon the houses where you are; and when I see the blood, I will pass over you, and no plague shall fall upon you to destroy you, when I smite the land of Egypt. (Ex. 12:13)
Jesus, who called himself "the Lamb of God" as one way of describing himself, was given by God in perfection, without sin. Jesus death, at the time of the Passover celebration, was the sacrifice that was demanded by a just God to pay for the sins of humankind. However, the loving grace of God accepts Jesus's blood as payment for the sins of those who believe. They will not be condemned or destroyed, but will share in the Resurrection of Jesus.
Turn to Exodus 12:1-6. This is where the selection of the lamb to be sacrificed at Passover is first described. In verse 3, it says that the lamb will be selected on the 10th day of the first month in the Jewish calendar. This first month is called “Nisan.” The Passover was set to occur five days later, on the 14th day of the month.
Now, turn to John 12:1. There, we read that Jesus went to Bethany “six days before the Passover.” Jesus goes there so that he can raise Lazarus from the dead.
In John 12:12-13, we read that “On the next day, the large crowd who had come to the feast, when they heard that Jesus was coming to Jerusalem, took the branches of the palm trees and went out to meet Him.” (NASB).
Notice that because it is “the next day,” this is the 10th of Nissan, the same day that the Jews were to select the Lamb for Passover. Because the crowds laid down palm branches, the Christian calendar calls this “Palm Sunday.”
Read Luke 19:36-44. Here is the story of Jesus riding into Jerusalem on a donkey. He is offering himself as “the Lamb of God who takes away the sins of the world,” but they wanted a political savior who would lead a rebellion against the Romans. It is for this reason that Jesus wept in Luke 19:41, and then talks about how the Jews had misunderstood the reason for his coming, saying (vs. 42): “If you had known in this day, even you, the things which make for peace!” (NASB)
Jesus came on “Lamb Selection Day” to offer himself as a sacrifice to atone for sin, and we missed it!