Hebrews 6-9

 If we ever have to remind ourselves why Jesus had to die to save us from our sins, this is the scripture that helps us.  The shedding of blood of animals under the old covenant was a powerful way of demonstrating forgiveness.  But it had to be done over and over and still did not cleanse the conscience.  Jesus' sacrifice is the one and only sacrifice that will purify us and cleanse us for eternity.