Why is there a need for a perfect sacrifice? Why does Jesus have to be perfect? Theologically, why was it necessary that Jesus be perfect? Couldn’t there be another ordinary human who said “I will be the sacrifice and take on all the sins of the world past, present, and future and suffer and die as a substitutionary atonement for all of mankind”? Why did it have to be Jesus and why did it have to be a perfect Jesus?
According to the levitical priesthood a sacrifice had to be without defect


  Lev 22:20 Do not bring anything with a defect, because it will not be
  accepted on your behalf.


In this case any sacrifice offered to God has to be without defect. We humans are born into sin and no one lives a life without sin. Romans 3:23 tells us we have all sinned and fallen short of the glory of God. Sin is bad because it separates us from God.


  Isaiah 59:2  But your iniquities have separated you from your God;
  your sins have hidden his face from you, so that he will not hear.


So ideally God would not accept any sacrifice by any man since sin  has already made them impure. The one person who lived without sin was Jesus so He was the only one capable of being offered as an acceptable sacrifice