The LORD said to Moses, "Consecrate to me all the firstborn. Whatever is the first to open the womb among the people of Israel, both of man and of beast, is mine." Then Moses said to the people, "Remember this day in which you came out from Egypt, out of the house of slavery, for by a strong hand the LORD brought you out from this place. No leavened bread shall be eaten. Today, in the month of Abib, you are going out. And when the LORD brings you into the land of the Canaanites, the Hittites, the Amorites, the Hivites, and the Jebusites, which he swore to your fathers to give you, a land flowing with milk and honey, you shall keep this service in this month. Seven days you shall eat unleavened bread, and on the seventh day there shall be a feast to the LORD. Unleavened bread shall be eaten for seven days; no leavened bread shall be seen with you, and no leaven shall be seen with you in all your territory.
Exodus 13:1-7
These verses complete, as it were, the meaning and significance of the Passover ordinance. The firstborn of Israel received substitutionary protection in the blood of the lamb that was slain, but this laid them under an incalculable debt to God and confirmed their obligation to live for Him. In effect, the firstborn of Israel had no right to be alive at all; that they were was due entirely to divine mercy and provision, and therefore God could say of them, 'They are Mine'. This is the sentiment that Paul echoes in more than one place in his epistles: 'Ye are not your own, for ye are bought with a price' (1 Corinthians 6:19, 20) and 'He died for all, that they which live should not henceforth live unto themselves but unto Him Who died for them and rose again' (2 Corinthians 5:15). God intended that by receiving the Passover His people would be united with its true meaning, and be separated unto Him. This is something we dare not forget in our understanding of the gospel. The Cross lays upon us a total demand, and makes a total claim upon our lives. To taste therefore of the Cross's power and virtue without the recognition that we thereby become unalterably God's is to rob Him of what is rightfully His. No understanding of redemption which falls short of this has any warrant for supposing it has a biblical basis.