It is a commandment that was given to the Israelites. Heb. 9:10 talks about carnal ordinances that were in place before the time of reformation. This means that these ordinances or statues imposed on Israelites had a time of reformation when it will be superceded by other laws.
This is what Apostle Paul refers to in Heb. 7:12 where he talks of a need to change the law since the priesthood has been changed.
The priesthood that was changed is that of Moses as stated in Heb. 3:1-3. Jesus Christ is the high priest that replaced Moses.
Apostle Paul was actually talking to the Hebrews who had become Christians, not those who remained under the law of Moses. He was saying that our Lord Jesus Christ is our priest who was found faithful by God.
And Acts 13:39 talks of the new law which is justification of all things by believers who could not be justified by the law of Moses.
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