ISB ~ Hebrews 7 v12

change in the priesthood:Insofar as Ps 110:4 envisions a change from the Levitical priesthood of Aaron to the Melchizedekian priesthood of Christ, it follows that the Mosaic laws of worship must also give way to the messianic laws of worship (7:18-19). Essentially this is a change from sacrificial rites that involve the blood of animals (10:4) to sacramental rites such as Baptism (10:22) and the Eucharist (6:4; 13:10), whose efficacy derives from the blood of Christ (9:11-14). In all probability, the maxim that a new priesthood brings new laws is based on a pattern established in the Bible. In fact, when the family priesthood of patriarchal times gave way to the clerical priesthood of Aaron in Mosaic times, this change was followed by the promulgation of an extensive code of law concerning the rites of liturgical worship (mainly in the Book of Leviticus). For more details, see essay: Priesthood in the Old Testament at Num 18.