Then Moses summoned all the elders of Israel and said to them, “Go at once and select the animals for your families and slaughter the Passover lamb. Take a bunch of hyssop, dip it into the blood in the basin and put some of the blood on the top and on both sides of the doorframe. None of you shall go out of the door of your house until morning. When the LORD goes through the land to strike down the Egyptians, he will see the blood on the top and sides of the doorframe and will pass over that doorway, and he will not permit the destroyer to enter your houses and strike you down. (Exodus 12:21-23 NIV)
When the last plague was about to happen, God told the Israelites to kill a lamb and smear the blood over the door posts. If they did this, the angel of death would pass over their homes and the first born of their families would be spared. Was it hard for them to reconcile that only the blood of the lamb spared their lives? Is it hard for us to reconcile that today?