…in whom we have redemption through His blood, the forgiveness of sins. Col 1:14

In order for a person of the Old Testament to get redemption, one must bring a substitution.
For instance, you redeemed a firstborn donkey with a lamb. (Ex 13:13). You sacrificed the lamb so the donkey would live.
But you sacrificed a firstborn lamb.
The difference between the two animals being the donkey is unclean and could not be sacrificed, whereas the lamb is a clean animal and could be sacrificed.
Firstborn male children needed dedicating to the Lord.
The Bible makes it abundantly clear that people are unclean and sinful. No one has done good and all have sinned and come short of God’s glory.
Clean animals sacrificed for us could never completely take away our sin. Heb 10:3-4 says in those sacrifices there is a reminder of sins every year. For it is not possible that the blood of bulls and goats could take away sins.
So Christ came as a man and as the Lamb of God to take away your sin.
Under the Law the perpetrator of sin must bring his own sacrifice for sin. You could not sit off in the distance and claim that since Bob’s sin was the same as yours, and Bob was already taking a sacrifice, that you’d just claim his sacrifice too.
Bob’s sacrifice only covered him, not you.
The same holds true about Jesus – His sacrifice only redeems you when you come to God in acceptance of it. You are not covered by my acceptance and I am not covered by your acceptance.
You come in faith to Him believing His redemption for you –
without faith it is impossible to please Him, for he who comes to God must believe that He is, and that He is a rewarder of those who diligently seek Him. Heb 11:6