For the priesthood being changed, of necessity there is also a change of the law - Hebrews 7:12. Scripture clearly just showed a few verses before what the law was that it was talking about = And indeed those who are the sons of Levi, who receive the priesthood, have a commandment to receive TITHES from the people according to the LAW... - Hebrews 7:5. Here mortal men receive tithes... - Hebrews 7:8. Even Levi, who receives tithes, paid tithes... - Hebrews 7:9. For on the one hand there is an annulling of the former commandment because of its weakness and unprofitableness - 7:18. The ONLY commandment mentioned in Scripture there is the tithe commandment. So the commandment that was annulled (v.18) is the tithe commandment.