The passage listed in Leviticus above describes the institution of the remembrance of the Passover and the Feast of Unleavened Bread that directly follows it. In order to understand this remembrance, we must look back to the first Passover, in Exodus 12.
The first verse of that passage says that this is to be their first month. God was telling the Israelites that what He was doing here was of paramount importance. This would be the event they set their calendars to. And this would be a great and new thing, a new beginning at the beginning of a new year.
Next, the Israelites were told to take a lamb on the 10th day. This lamb was to be selected – chosen with a purpose – and to be without any blemish, looking forward to Christ who was the spotless Sacrifice. Many years later, when Christ came, this would be the day He entered Jerusalem.
They were to keep the lamb until the 14th day (the day Christ would die). This gave them time to ensure that it really was a perfect sacrifice. Then they were to kill the lamb at evening (about the time Christ died).
They were to roast the lamb whole, signifying Christ’s wholeness and perfection, and were to eat it in haste, remembering their deliverance from Egypt.
The lamb was to be eaten with unleavened bread. Leaven frequently is a symbol for sin; the Israelites were leaving sin behind in Egypt. They ate with bitter herbs, to remind them of the hardness and bitterness of sin.
The blood of the lamb was to be placed over and beside the door posts. They had to be “under the blood”, as we have to be covered by the blood-sacrifice of Christ today.
In verse 14 of Exodus 12, God told the Israelites that He was instituting a memorial that would be celebrated yearly until it was fulfilled in Christ. Furthermore, God told them to be sure to keep this as a reminder to their children (v 26, 27) and be ready to explain the significance of the ritual to them. In the same way, we should be constantly teaching our children the glorious gospel of Christ.