The "Passover" was not in remembrance for the Exodus

[RND]

Exd 12:12 For I will pass through the land of Egypt this night, and will smite all the firstborn in the land of Egypt, both man and beast; and against all the gods of Egypt I will execute judgment: I [am] the LORD. 13 And the blood shall be to you for a token upon the houses where ye [are]: and when I see the blood, I will pass over you, and the plague shall not be upon you to destroy [you], when I smite the land of Egypt.

A study from a Messianic Jew:

The Passover

This was the reason for the observance of the Passover! The Passover happened prior to the exodus from Egypt, not after. The Passover is not a remembrance of the escape out of Egypt, it is the remembrance for the blood that God was willing to shed on behalf on His people.

"Here was a work required of the children of Israel, which they must perform on their part, to prove them and to show their faith by their works in the great deliverance God had been bringing about for them. In order to escape the great judgment of God which he was to bring upon the Egyptians, the token of blood must be seen upon their houses. And they were required to separate themselves and their children from the Egyptians, and gather them into their own houses, for if any of the Israelites were found in the houses of the Egyptians, they would fall by the hand of the destroying angel. They were also directed to keep the feast of the passover for an ordinance, that when their children should inquire what such service meant, they should relate to them their wonderful preservation in Egypt. That when the destroying angel went forth in the night to slay the first-born of man, and the first-born of beast, he passed over their houses, and not one of the Hebrews was slain that had the token of blood upon their door-posts. And the people bowed their heads and worshiped, grateful for this remarkable memorial given to preserve to their children the remembrance of God's care for his people.

There was quite a number of Egyptians who were led to acknowledge, by the manifestations of the signs and wonders shown in Egypt, that the God of the Hebrews was the only true God. They entreated to be permitted to come to the houses of the Israelites with their families, upon that fearful night when the angel of God should slay the first-born of the Egyptians. They were convinced that their gods whom they had worshiped were without knowledge, and had no power to save or to destroy. And they pledged themselves to henceforth choose the God of Israel as their God. They decided to leave Egypt, and go with the children of Israel to worship their God. The Israelites welcomed the believing Egyptians to their houses. {3SG 223.1}

The passover pointed backward to the deliverance of the children of Israel, and was also typical, pointing forward to Christ, the Lamb of God, slain for the redemption of fallen man. The blood sprinkled upon the door-posts pre-figured the atoning blood of Christ, and also the continual dependence of sinful man upon the merits of that blood for safety from the power of Satan, and for final redemption. Christ ate the passover supper with his disciples just before his crucifixion, and the same night instituted the ordinance of the Lord's supper, to be observed in commemoration of his death. The passover had been observed to commemorate the deliverance of the children of Israel from Egypt. It had been both commemorative and typical. The type had reached the antitype when Christ, the Lamb of God without blemish, died upon the cross. He left an ordinance to commemorate the events of his crucifixion." {3SG 225.1}

The observance of the Passover began with the birth of the Hebrew nation. On the last night of their bondage in Egypt, when there appeared no token of deliverance, God commanded them to prepare for an immediate release. He had warned Pharaoh of the final judgment on the Egyptians, and He directed the Hebrews to gather their families within their own dwellings. Having sprinkled the doorposts with the blood of the slain lamb, they were to eat the lamb, roasted, with unleavened bread and bitter herbs. "And thus shall ye eat it," He said, "with your loins girded, your shoes on your feet, and your staff in your hand; and ye shall eat it in haste: it is the Lord's passover." Ex. 12:11. At midnight all the first-born of the Egyptians were slain. Then the king sent to Israel the message, "Rise up, and get you forth from among my people; . . . and go, serve the Lord, as ye have said." Ex. 12:31. The Hebrews went out from Egypt an independent nation. The Lord had commanded that the Passover should be yearly kept. "It shall come to pass," He said, "when your children shall say unto you, What mean ye by this service? that ye shall say, It is the sacrifice of the Lord's passover, who passed over the houses of the children of Israel in Egypt, when He smote the Egyptians." Thus from generation to generation the story of this wonderful deliverance was to be repeated. {DA 76.1}