Part of that is obvious. The other part, to me, had remained hidden. I suspect I have the pagan holiday, Easter, to thank for that. While knowing it to be pagan, it was nevertheless a distraction from the real issue.
The first passover was when God redeemed the Israelites, His chosen people, out of the power and land of Pharaoh. God sent ultimate destruction on every aspect of the Egyptians lives, but it was not until blood was shed that Pharaoh lost. (Exodus 12)
God was going to kill the firstborn of every man and beast in Egypt, except those who believed His Word, and killed a lamb, smearing it's blood on the door. The Israelites were saved by the sacrifice - not only their firstborn, but the entire people.
But what is the significance of the firstborn?
