Passover.
Exodus 12:12 “On that same night I will pass through Egypt and strike down every firstborn of both people and animals, and I will bring judgment on all the gods of Egypt. I am the Lord. 13 The blood will be a sign for you on the houses where you are, and when I see the blood, I will pass over you. No destructive plague will touch you when I strike Egypt.
At the first Passover each family was instructed to take a year-old spotless lamb - one per household (depending on the size of the household).
The animal chosen had to be without defect, and since the Passover lamb was symbolic of Christ, it symbolised being without sin. The Lamb was a shadow of Christ our Passover lamb, and a shadow is a representation of the real thing, so this lamb showed people the type of sacrifice that was to come.
God instructed the Israelites to slaughter the lamb at twilight and apply some blood along the top of their doorposts as well as to both sides. These had to be the doorposts of the houses where they ate the lambs. Likewise, we can only be covered by the blood of Jesus if we have first partaken of him or accepted Him as our Lord and Saviour.
When the Lord came that night he was only looking for one thing: blood on the doorposts. It was a simple as that! God did not look at the people inside the house at all. It was irrelevant whether or not they were religious and kept the commandments, good people, or completely the opposite. It didn't matter about the people inside the house - only the blood on the doorposts was important. If there was blood on the doorpost, the household inside was safe, but if not, they were condemned to lose their firstborn son.
The significance for us is that Jesus became our passover lamb, and now His blood is the only thing that God is looking for. We don't have to be sin conscious or performance conscious. God will judge us based on whether we are covered by the blood of Jesus alone. It really doesn't matter how good or sinful we are, because it's not about us.
That is good news for those who have accepted Christ as their saviour, and must be spread to the lost who need to hear it.