What would have happened to the Israelites if they had refused to put the blood on the door?
If the Israelites had refused to put the blood on the door, they would not have been safe; they would also have lost their firstborn. Their safety rested solely on the blood applied by faith, not on their goodness, and every Jewish household in Goshen evidently complied.
Les explains that the Israelites in Goshen were absolutely secure, not because of anything they had earned or their goodness, but because of the blood on the door. That was an act of faith. If they had scoffed and refused, asking what three little globs of blood could do, they would not have been safe; they too would have lost their firstborn. Scripture gives no indication that any Jews were lost, but evidently every Jewish household in Goshen had the blood applied and was safe. Les qualifies that being under the blood does not give license, yet it made them totally safe and secure, just as those under the blood are secure. He also notes this whole exodus from Egypt was God's redemption of the nation.