What does Exodus 13:13 mean?
Israel has been told that when they enter the Promised Land (Exodus 13:11), they are to consecrate every firstborn to God (Exodus 13:1–2, 12). This applied to the first male born to a given woman or animal; this male was considered the Lord's. In the case of animals, this would mean sacrifice. Human firstborn were to be "redeemed" by sacrificing a lamb, instead. The prophet Samuel was a rare case where the firstborn was not kept with the family but instead fully given to God for a lifetime of service (1 Samuel 1:11, 26–28).Donkeys were common and valuable animals in the ancient world. However, they were not suitable for sacrifice under the old covenant. Later laws will define donkeys as "unclean" for the purposes of food (Leviticus 11:2–4). This also meant they could not be sacrificed to God. Such animals were to be killed by breaking the neck, rather than the sacrificial process of bleeding.
Further instructions regarding redemption of sons is later given. Some instructions are related to the Levites shortly after the exodus (Numbers 3:40–48) and others are more general related to practices for future generations (Numbers 18:15–16).