Over the years I've heard a lot of people make the comment that God is all about rules. If nothing else, this passage regarding Israel's exodus from Egypt shows that God establishes a relationship with people before he expects them to obey rules. God didn't give the Ten Commandments to the Israelites and demand obedience before leading them out of slavery. To the contrary, he first led them out of slavery because of their act of trust.
Following God has always been about an act of trust – just as much before as it is now. The Israelite's profession of faith and act of trust was in the blood of the lamb that was painted on the doorposts of their homes. They were trusting that God would spare them because of their act of faith. For us, we are also trusting in the shed blood of a lamb, but this time it's the Lamb of God – Jesus – who was slain for the sins of the world. The Israelites didn't realize that their act of trust was simply a foreshadowing of our act of trust in Christ.