Revelation 1:6

And hath--rather as Greek, "And (He) hath." made us kings--The oldest manuscripts read, "a kingdom." One oldest manuscript reads the dative, "for us." Another reads "us," accusative: so Vulgate, Syriac, Coptic, and ANDREAS. This seems preferable, "He made us (to be) a kingdom." So Exo 19:6, "a kingdom of priests"; Pe1 2:9, "a royal priesthood." The saints shall constitute peculiarly a kingdom of God, and shall themselves be kings (Rev 5:10). They shall share His King-Priest throne in the millennial kingdom. The emphasis thus falls more on the kingdom than on priests: whereas in English Version reading it is equally distributed between both. This book lays prominent stress on the saints' kingdom. They are kings because they are priests: the priesthood is the continuous ground and legitimization of their kingship; they are kings in relation to man, priests in relation to God, serving Him day and night in His temple (Rev 7:15; Rev 5:10). The priest-kings shall rule, not in an external mechanical manner, but simply in virtue of what they are, by the power of attraction and conviction overcoming the heart [AUBERLEN]. priests--who have pre-eminently the privilege of near access to the king. David's sons were priests (Hebrew), Sa2 8:18. The distinction of priests and people, nearer and more remote from God, shall cease; all shall have nearest access to Him. All persons and things shall be holy to the Lord.

— Jamieson-Fausset-Brown Commentary (public domain)