Hebrews 7:12

The priesthood being changed - That is, The order of Aaron being now abrogated, to make way for that which had preceded it, the order of Melchisedec.

There is made of necessity a change also of the law - The very essence of the Levitical law consisting in its sacrificial offerings; and as these could not confer perfection, could not reconcile God to man, purify the unholy heart, nor open the kingdom of heaven to the souls of men, consequently it must be abolished, according to the order of God himself; for he said, Sacrifice and offering, and burnt-offering, and sacrifice for sin, he would not; see Psalm 40:6, Psalm 40:7, compared with Hebrews 10:5-10, and with Psalm 110:4, where it is evident God designed to change both the law and the priesthood, and to introduce Jesus as the only Priest and Sacrifice, and to substitute the Gospel system for that of the Levitical institutions. The priesthood, therefore, being changed, Jesus coming in the place of Aaron, the law of ordinances and ceremonies, which served only to point out the Messiah, must of necessity be changed also.

For the priesthood being changed - According to the prediction in Psalm 110. that it would be. When that occurs, the consequence specified will also follow.

There is made of necessity a change also of the law - The Law so far as it grew out of that, or was dependent on it. The connection requires us to understand it only of the Law "so far as it was connected with the Levitical priesthood." This could not apply to the ten commandments - for they were given before the institution of the priesthood; nor could it apply to any other part of the moral law, for that was not dependent on the appointment of the Levitical priests. But the meaning is, that since a large number of laws - constituting a code of considerable extent and importance - was given for the regulation of the priesthood, and in reference to the rites of religion, which they were to observe or superintend, it followed that when their office was superseded by "one of a wholly different order," the Law which had regulated them vanished also, or ceased to be binding. This was a very important point in the introduction of Christianity, and hence, it is that it is so often insisted on in the writings of Paul. The argument to show that there had been a change or transfer of the priestly office, he proceeds to establish in the sequel.

7:12 For - One of these cannot be changed without the other.