Hebrews 10:4 For it is not possible that the blood of bulls and goats could take away sins.

You may wonder “why do it?” or “why did God require it?”
It was an act of faith and obedience on the part of the Hebrews.
The chapter starts with “for the law, having a shadow of the good things to come, and not the very image of the things, can never with these same sacrifices, which they offer continually year by year, make those who approach perfect.” (Hebrews 10:1)
The shadow is not the item casting it.
In this case, the Law is the shadow of Christ.
The attempt to keep the Law was the act of faith of the Hebrews under the Law.
Their sacrifices were the acts of faith pointing to the sacrifice to come in Jesus Christ.
We are no longer under the Law, since Christ came and fulfilled the Law in Himself and sacrificed Himself once and for all.
What is your act of faith today?
Accepting Christ as your Savior, a public profession of your faith, baptism, Communion, and church fellowship are all acts of faith in what Jesus has done for you.