What does Exodus 11:5 mean?
God promised to use powerful signs to free Israel from slavery (Exodus 3:20). Nine catastrophes have not convinced the Pharaoh (Exodus 7:21; 8:6, 17, 24; 9:6, 10, 24; 10:14, 23). Instead, he has threated to kill God's spokesman (Exodus 10:28–29). Moses is responding with the Lord's dire warning (Exodus 11:4). Egypt will suffer the death of their firstborn—all of their firstborn.The term "firstborn" translates the Hebrew root word bekōr. This refers to the primary heir or most important descendant. Typically, this heir is literally the "first born:" the oldest son. Those not the eldest male child can also become "firstborn" if the heir dismisses their birthright (Genesis 25:31–32; Hebrews 12:16) or commits serious evil (Genesis 49:3–4). The firstborn represents the legacy, strength, and hopes of their ancestors.
Moses makes it clear that this stroke of death will apply to every person and animal in Egypt. Livestock, servants, and even the royal family's heir are to suffer. This is the threat God said Moses would deliver when he was first sent on this mission (Exodus 4:21–23). Pharaoh has ignored the suffering of others and threatened to kill Moses. As a result, he will suffer and see his own son die.