Revelation 20:6b …but they shall be priests of God and of Christ, and shall reign with him a thousand years.
The promise that the people of God will be priests and kings goes back to Moses when the Lord established the Covenant with the people at Mt. Sinai: ”you shall be a kingdom of priests [Exodus 19:6].” Actually, the promise goes back to when Adam (all people) was created to ”have dominion,” rule over and care for Creation. The promise is repeated until it is restored in Christ and the Church.
God promises that we will be priests and reign forever, and the kingdom starts now. The ”thousand years” covers all the time between the Ascension and the Second Coming. In Christ, and with Christ, and with Christ in us, we live to bless, serve, protect, and care for all created things, including other people.
When we were baptized we became kings to rule over Evil, and priests to pray for others and be ”little Christs” to them. We became the salt of the earth and the light of the world. We don’t even know the impact of our lives on the world around us through prayer, service, love, acts of kindness, forgiveness, resisting the devil, taking authority over sin and evil. We make a difference. Since we don’t see it, we are given the promise that we are priests and kings, so that we may believe it to be so. If we saw what effect we have we would become puffed up and proud, and thus mess up our functions as kings and priests.
Jesus is our High Priest and King of kings, and He exercises priestly and kingly functions through us as a kingdom of priests. Our focus is always to be on Christ and His Gospel, and His promise is that we will be priests of God and we will reign with Christ. Take His word for it and enjoy serving.