15 For when Pharaoh stubbornly refused to let us go, the Lord slew all the first-born in the land of Egypt, both the first-born of man and the first-born of cattle. Therefore I sacrifice to the Lord all the males that first open the womb; but all the first-born of my sons I redeem.'
Matthew Henry's Commentary on Exodus 13:15
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.