12 you are to set aside the first birth out of every womb to God. Every first birth from your livestock belongs to God. 13 You can redeem every first birth of a donkey if you want to by substituting a lamb; if you decide not to redeem it, you must break its neck. 14 When the time comes and your son asks you, 'What does this mean?' you tell him, 'God brought us out of Egypt, out of a house of slavery, with a powerful hand. 15 When Pharaoh stubbornly refused to let us go, God killed every firstborn in Egypt, the firstborn of both humans and animals. That's why I make a sacrifice for every first male birth from the womb to God and redeem every firstborn son.'
Matthew Henry's Commentary on Exodus 13:12-15
Commentary on Exodus 13:11-16
(Read Exodus 13:11-16)
The firstlings of beast not used in sacrifice, were to be changed for others so used, or they were to be destroyed. Our souls are forfeited to God's justice, and unless ransomed by the sacrifice of Christ, will certainly perish. These institutions would continually remind them of their duty, to love and serve the Lord. In like manner, baptism and the Lord's supper, if explained and attended to, would remind us, and give us occasion to remind one another of our profession and duty.