Let’s consider another major change in the Law that has taken place. It is plainly taught in the Law (Numbers 1:48-53) that no one can be a priest except those of the lineage of the three sons of Levi which make up the tribe of Levi. The three sons are Gershon, Kohath, and Merari. The Lord appointed the descendants of each son a specific role in the priesthood and for the function of the Tabernacle/ Temple; Gershon (Numbers 3:25-26), Kohath (Numbers 3:31), Merari (Numbers 3:36-37). But in addition to these appointments, the actual priestly office that offered up the sacrifices and were allowed to touch the holy things was given only to Moses (not his sons) and more specifically to Aaron and his sons (Numbers 3:38). Because it was appointed to Aaron and his sons alone to touch the holy things within the Tabernacle, they would have to cover the holy things with blue cloth before the Kohathites (who were also Levites) could move any of them; lest they die:

   Numbers 4:15  And when Aaron and his sons have made an end of covering the sanctuary, and all the vessels of the sanctuary, as the camp is to set forward; after that, the sons of Kohath shall come to bear it: but they shall not touch any holy thing, lest they die. These things are the burden of the sons of Kohath in the tabernacle of the congregation. 
 

Therefore, we understand that no one but the Levites could serve in the priesthood because anyone else would die. And only the sons of Aaron of the Levities could offer up the sacrifices; anyone else including other Levites not of the sons of Aaron would die. Having established all this, the purpose is to convey the seriousness and responsibility of being a priest. No one was to take this role upon himself except those of the tribe of Levi.
So, let’s consider how this law regarding the priesthood has changed:

    Hebrews 7:11-12  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? 12 For the priesthood being changed, there is made of necessity a change also of the law.

Jesus, who was of the tribe of Judah and not of the tribe of Levi (and specifically not of the order of Aaron), could not serve as a priest according to the Law of Moses. Therefore, the Law of Moses had to be changed:

   Hebrews 7:14 -18  14 For it is evident that our Lord sprang out of Juda; of which tribe Moses spake nothing concerning priesthood. 15 And it is yet far more evident: for that after the similitude of Melchisedec there ariseth another priest, 16 Who is made, not after the law of a carnal commandment, but after the power of an endless life. 17 For he testifieth, Thou art a priest for ever after the order of Melchisedec. 18 For there is verily a disannulling of the commandment going before for the weakness and unprofitableness thereof.

The word “disannulling” in the Greek means “cancellation”:

   (Strong’s) 115  athetesis ath-et'-ay-sis
   from 114; cancellation (literally or figuratively):--disannulling, put away.

The understanding for the use of this word requires no explanation. The fact has been established that the priesthood has changed and the Law concerning the Levitical appointment has been cancelled. Who changed that law? It was Messiah and this point has been covered in a paper titled “The Final Lawgiver”. This change has made it possible for people from the other tribes not just Levi to serve as priests. But in addition to the twelve tribes of Israel, now there are entered into the priesthood, people from “every kindred, and tongue, and people, and nation”. And who made that change? It was Messiah:

   Revelations 1:4-6  4 John to the seven churches which are in Asia: Grace be unto you, and peace, from him which is, and which was, and which is to come; and from the seven Spirits which are before his throne; 5 And from Jesus Christ, who is the faithful witness, and the first begotten of the dead, and the prince of the kings of the earth. Unto him that loved us, and washed us from our sins in his own blood, 6 And hath made us kings and priests unto God and his Father; to him be glory and dominion for ever and ever. Amen

   Revelations 5:8-10   8 And when he had taken the book, the four beasts and four and twenty elders fell down before the Lamb, having every one of them harps, and golden vials full of odours, which are the prayers of saints. 9 And they sung a new song, saying, Thou art worthy to take the book, and to open the seals thereof: for thou wast slain, and hast redeemed us to God by thy blood out of every kindred, and tongue, and people, and nation; 10 And hast made us unto our God kings and priests: and we shall reign on the earth.

It is Messiah who has changed the Law and made us priests where once according to the Law of Moses we could not be priests because we were not of the tribe of Levi. But now, Christ has “ out of every kindred, and tongue, and people, and nation” taken of us to be priests. But Christ has also made us kings as well. In contrast, Levites never served or were ever appointed as kings in the history of Israel. If some should argue that this reference to us being priests is not to take effect until we reach heaven, then they would be wrong:

    1Peter 2:4-10  4 To whom coming, as unto a living stone, disallowed indeed of men, but chosen of God, and precious, 5 Ye also, as lively stones, are built up a spiritual house, an holy priesthood, to offer up spiritual sacrifices, acceptable to God by Jesus Christ. 6 Wherefore also it is contained in the scripture, Behold, I lay in Sion a chief cornerstone, elect, precious: and he that believeth on him shall not be confounded. 7 Unto you therefore which believe he is precious: but unto them which be disobedient, the stone which the builders disallowed, the same is made the head of the corner, 8 And a stone of stumbling, and a rock of offence, even to them which stumble at the word, being disobedient: whereunto also they were appointed. 9 But ye are a chosen generation, a royal priesthood, an holy nation, a peculiar people; that ye should shew forth the praises of him who hath called you out of darkness into his marvellous light; 10 Which in time past were not a people, but are now the people of God: which had not obtained mercy, but now have obtained mercy.

Peter is writing to the church present on the earth in his time saying “ye are a holy priesthood”, “a royal priesthood” and how could that be possible under the Law of Moses? It could not happen; therefore, we understand that Messiah has changed the Law. Otherwise, New Covenant believers could not be referred to as priests. Under the Law of Moses, Gentiles could never have been admitted to the priesthood in any capacity.
How does this significant and undeniable change not qualify as “one jot or one tittle” passing from the Law?