What does Exodus 11:6 mean?

This describes how Egypt will react to the tenth and final disaster (Exodus 7:21; 8:6, 17, 24; 9:6, 10, 24; 10:14, 23) resulting from their enslavement of the Israelites (Exodus 1:11–14). Moses has been threatened by the Egyptian pharaoh (Exodus 10:28–29) for not accepting a partial release of the slaves (Exodus 10:25–26). In response, Moses delivers the Lord's dire promise (Exodus 4:21–23) that during the night He will kill all the firstborn in Egypt (Exodus 11:4–5). This would forever be known as the most devastating event in Egypt's history (Exodus 12:30). Later information given to Israel suggests that there were at least several days between Moses' declaration and the coming of the plague (Exodus 12:3–6).

The primary heir, usually the oldest son, is described using the word "firstborn." This translates the Hebrew root word bekōr. Others could become the "firstborn" without literally being the earliest-born if the intended heir somehow lost their right to the title (Genesis 25:31–32; 49:3–4; Hebrews 12:16). In ancient culture, descendants were a person's legacy, security in old age, and so forth. Beyond emotional bonds, the firstborn also represented any hope for the future. Such a loss would be terrible for any family and shattering if it happened to an entire culture. This plague will strike every firstborn of Egypt, making no exception for animals, servants, or even royalty (Exodus 11:5).

In contrast, the people of Israel will experience no effects from this plague (Exodus 11:7). Those who fear the Lord will be given a sign to avoid judgment (Exodus 12:13).