By faith he kept the Passover and the sprinkling of blood, so that the destroyer of the firstborn would not touch the firstborn of Israel. Hebrews 11:28
The slaying of the firstborn in Egypt was the final plague against Pharoah and the Egyptians. Before this, no human blood had been shed. Now, though, Moses painted the blood of a Passover lamb around the doors to all Israelite dwellings. Then they were to wait all night before going out. Exodus 12:30 tells us there was a great cry throughout the land as the firstborn were slain.
I confess I'm more than a little troubled by this particular passage. I look at it 4000 years removed and wonder why the Lord had to take the lives of so many innocent children. I suspect that as Moses and the Israelites listened to their neighboring Egyptians wailing all night, it took faith just to wait and sort it all out the next morning. They had to have faith that the Lord knew what he was doing when He went to such extremes on their behalf.
I guess not a lot has changed over the years. It takes faith just to acknowledge that God knows what he's doing in our lives and in the crazy out-of-control world we live in. I've written it before in this space, but many of these issues arise so that we make seek Him, for He is the one who knows the answers. If we had all the answers, we probably wouldn't need to go to God.