The Bible speaks of the ministry of the priesthood. This ministry consists of a group of people wholly separated from the world to serve God. They have no other occupation or duty other than to serve God. Such people are called priests in the Bible.
Beginning from the book of Genesis, we find God calling men to be priests. Melchisedec was God's first priest. In Abraham's time, Melchisedec separated himself and gave himself solely to God's service.
From Genesis to the forming of the nation of Israel and thereafter, the priesthood was always present. At the time the Lord Jesus was on earth and even after His departure from the earth, the priesthood did not cease. The priesthood has been on earth for a long time. The Bible shows us that even the Lord Jesus became a priest before God after His ascension to the heavens. He is there now fully consecrated for God's service.
The priesthood continues throughout the dispensation of the church; there is no interruption of any kind.
At the beginning of the millennial kingdom, those who share in the first resurrection will be priests of God and of Christ and will reign with Him for a thousand years (Rev. 20:6). God's children will continue to be God's priests and Christ's priests for a thousand years. They will be kings to the world and priests to God. This priesthood will remain unchanged; they will still serve God.
In the new heavens and new earth, the term priest will cease to exist. At that time, all of God's children as His servants will do nothing except serve Him. In the New Jerusalem "His slaves will serve Him" (22:3). In other words, God's children will continue to serve Him.
Here we must point out a most wonderful thing. The priesthood commenced with Melchisedec, the one who was without father, without mother, without genealogy, who had neither beginning of days nor end of life (Heb. 7:3), and it extends to the end of the millennium, which means that it extends to eternity.