Hebrews 10:2-4 KJVS
For then would they not have ceased to be offered? because that the worshippers once purged should have had no more conscience of sins. [3] But in those sacrifices there is a remembrance again made of sins every year. [4] For it is not possible that the blood of bulls and of goats should take away sins.
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Hebrews 9:12-14 KJVS
Neither by the blood of goats and calves, but by his own blood he entered in once into the holy place, having obtained eternal redemption for us . [13] For if the blood of bulls and of goats, and the ashes of an heifer sprinkling the unclean, sanctifieth to the purifying of the flesh: [14] How much more shall the blood of Christ, who through the eternal Spirit offered himself without spot to God, purge your conscience from dead works to serve the living God?
Now in the old testament or covenant, there was what is called the sin offering. It was done to ask God for forgiveness and remission of sin. But there was something incomplete about this sacrifice, the mind wasn't free from the guilt of sin. The result or outcome of the act(sin) committed was being avoided by the sacrifice but the thought of the act in the mind of the offender was retained. Hmm! It was a strong hold master minded by the devil to keep people in bondage. This is similar with some Christians toady, slaves to the guilt of their past and present faults.
Look at our second scripture Hebrews 9, it says the sacrifice made during the time of Moses and before the coming of Jesus, was made to purify the flesh. A means of justification for the man to be free from the physical act of sin committed but in reality, was still trapped in his mind. For this purpose, Jesus came and it says that the blood of Jesus can purge our minds and conscience frok every dead work of the flesh.