"And they sung a New Song, saying, Thou are 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; and hast made us unto our God Kings and Priests; and we shall reign on the earth."
Revelation 5:9-10

       This couldn't be said of angels or any other created heavenly beings.
        They haven't been redeemed by the Blood of the Lamb, nor are they to be Kings and Priests on the earth.