12 that thou shalt offer unto Jehovah all that breaketh open the womb, and every firstling that cometh of cattle which is thine: the males [shall be] Jehovah's. 13 And every firstling of an ass shalt thou ransom with a lamb; and if thou do not ransom it, thou shalt break its neck; and every firstborn of a man among thy sons shalt thou ransom. 14 And it shall be when thy son asketh thee in time to come, saying, What is this? that thou shalt say to him, With a powerful hand Jehovah brought us out from Egypt, out of the house of bondage. 15 And it came to pass, when Pharaoh stubbornly refused to let us go, that Jehovah slew all the firstborn in the land of Egypt, both the firstborn of men and the firstborn of cattle: therefore I sacrifice to Jehovah all that breaketh open the womb—being males; and every firstborn of my children I ransom.
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.