The First Passover Christian Art Sketch by Bertram Poole

The father of the house has killed the lamb and carefully put the blood in the basin.  Now using a bunch of hyssop he applies the blood to the doorposts and the lintel while the children look on.  His wife prepares the unleavened bread in the background.

Now, as long as they stay in the house and do not cross the threshold, they are protected.  When death sees the blood it "passes over" that house.

What is significant is that if an Isrealite had not heeded the warning and not applied the blood or ventured out from it's protection, he would have died, just the same as the Egyptians.

Jesus died on the eve of Passover (Pesach in Hebrew) and the Scriptures clearly state that He is our Passover Lamb, so His Blood protects us from spiritual death.