What does Exodus 13:15 mean?
Egypt had enslaved Israel (Exodus 1:11–14). When God sent Moses to lead the people to freedom (Exodus 3:10), the assignment came with a prediction of miracles. These would be needed specifically because the Egyptian king, the pharaoh, would be resistant to giving them freedom (Exodus 3:19–20). Pharaoh repeatedly refused the Lord's command to release the Hebrew slaves (Exodus 5:2; 7:12, 14, 22; 8:15, 19, 32; 9:7, 34; 10:10). At times, he even broke his word (Exodus 8:15, 31–32; 9:34–35; 10:19–20). Despite many supernatural signs (Exodus 7:21; 8:6, 17, 24; 9:6, 10, 24; 10:14, 23), Pharaoh was obstinate. It took the death of Egypt's firstborn (Exodus 11:4–6) to break him enough to allow Israel to go free (Exodus 12:29–32).These historic events are the reason Israel is being commanded to observe particular traditions (Exodus 12:14, 17, 24; 13:10). Consecrating the first male born to any woman or animal (Exodus 13:1–2, 12) recalled how the Lord took Egypt's firstborn but spared Israel because of sacrificial lambs (Exodus 12:12–13). Animals were to be sacrificed unless they were unclean (Exodus 13:13). Children were to be "redeemed" by sacrificing a lamb.
Exodus 13:11–16 expands on the command to consecrate all firstborn of Israel to the Lord. Every male which is the first birthed by any person or animal is considered God's. Animals may be sacrificed, but persons and animals that are to be kept must be "redeemed" by sacrificing a lamb. This reminds Israel of God's work on their behalf (Exodus 12:29–32). It also emphasizes the need for sacrifice in order to be reconciled to God.
God reiterates the requirements of the Feast of Unleavened Bread. Israel is to celebrate this every year as a way of remembering their liberation from Egyptian slavery. In addition, the people are to consecrate all of the first-born of any mother—both people and animals. Animals that cannot be sacrificed are to be redeemed. Sons are to be redeemed by an animal sacrifice. The Lord creates a column of clouds for the people to follow during the day, which is lit by fire so they can also follow it at night. This keeps them moving quickly. Soon, Egyptian soldiers will catch up to them and God will once again provide miraculous rescue (Exodus 14).