Why did the people redeem the firstborn animals?


The first offspring of every womb, both human and animal, that is offered to the Lord is yours. But you must redeem every firstborn son and every firstborn male of unclean animals. When they are a month old, you must redeem them at the redemption price set at five shekels of silver, according to the sanctuary shekel, which weighs twenty gerahs.  But you must not redeem the firstborn of a cow, a sheep or a goat; they are holy. Splash their blood against the altar and burn their fat as a food offering, an aroma pleasing to the Lord. Numbers 18:15-17
            “Redeem” means to pay the price to release something from bondage/slavery.  God set up a symbolic system that included:
1.      A firstborn
2.      Paying the price
3.      Freedom from slavery
Jesus would ultimately come as the firstborn son (of God and Mary) giving himself as an offering to pay the price of our sin to free us from the slavery to sin.  This firstborn theme would continue in the temple offerings until Jesus arrived and completed the theme through his death.  “It is finished…” Jesus declared.