Nevertheless, GOD disannulled the commandment.
Now, which Commandment did He disannul?
Heb 7:11 If therefore perfection were by the Levitical priesthood, (for under it the people received the law,) what further need was there that another priest should rise after the order of Melchisedec, and not be called after the order of Aaron?
Heb 7:12 For the priesthood being changed, there is made of necessity a change also of the law.
Heb 7:13 For he of whom these things are spoken pertaineth to another tribe, of which no man gave attendance at the altar.
Heb 7:14 For it is evident that our Lord sprang out of Juda; of which tribe Moses spake nothing concerning priesthood.
Heb 7:15 And it is yet far more evident: for that after the similitude of Melchisedec there ariseth another priest,
Heb 7:16 Who is made, not after the law of a carnal commandment, but after the power of an endless life.
Heb 7:17 For he testifieth, Thou art a priest for ever after the order of Melchisedec.
Heb 7:18 For there is verily a disannulling of the commandment going before for the weakness and unprofitableness thereof.
this one...
Num 18:1 And the LORD said unto Aaron, Thou and thy sons and thy father's house with thee shall bear the iniquity of the sanctuary: and thou and thy sons with thee shall bear the iniquity of your priesthood.
Num 18:2 And thy brethren also of the tribe of Levi, the tribe of thy father, bring thou with thee, that they may be joined unto thee, and minister unto thee: but thou and thy sons with thee shall minister before the tabernacle of witness.
Num 18:3 And they shall keep thy charge, and the charge of all the tabernacle: only they shall not come nigh the vessels of the sanctuary and the altar, that neither they, nor ye also, die.
Num 18:4 And they shall be joined unto thee, and keep the charge of the tabernacle of the congregation, for all the service of the tabernacle: and a stranger shall not come nigh unto you.
Num 18:5 And ye shall keep the charge of the sanctuary, and the charge of the altar: that there be no wrath any more upon the children of Israel.
Num 18:6 And I, behold, I have taken your brethren the Levites from among the children of Israel: to you they are given as a gift for the LORD, to do the service of the tabernacle of the congregation.
This is the Commandment that makes no mention of Judah but rather Levi in doing the service of God in the Temple. This is the Law that was changed. According to this Law, Christ could not be High Priest because He was not of the tirbe of Levi. Since Christ gave this Law, He has the authority to change it and He did. The Priesthood was changed from a Levitical Priesthood to the Melchisidec Priesthood. This is the Law that was changed.