Revelation 1:6

6 And hath made us kings and priests unto God and his Father; to him be glory and dominion for ever and ever. Amen.

John is talking about himself and all other believers. He says that Jesus has already made us kings and priests unto God by washing us in His blood. This is the destiny of the faithful Church. He does not say to become kings and priests we first must do all the requirements our denomination lays on us. John does not say we will become kings and priests if we live holy lives or persevere until we die. John says we are kings and priests because we were washed in His blood. In the tense John wrote this, all believers already have been born into a nation of kings and priests who will rule and reign with Christ.

The word dominion in this verse is not a good translation choice of words. Better choices from the Greek are "power" or "strength". The end of this verse should read,  " to Him be glory and power forever ".