The New Testament doctrine that all believers in Christ are priests offering spiritual sacrifices to God through Jesus Christ. The clearest statements are in 1 Peter 2:5, 9 — "you yourselves like living stones are being built up as a spiritual house, to be a holy priesthood, to offer spiritual sacrifices acceptable to God through Jesus Christ... you are a chosen race, a royal priesthood, a holy nation, a people for his own possession." The Reformation called this doctrine the priesthood of all believers — fundamental to recovering the gospel against Medieval Rome's insistence on a clerical priestly caste mediating between God and laity.
Spiritual priesthood has four major implications. (1) Direct access. Every believer approaches God directly through Christ, without the mediation of any earthly priest. "We have confidence to enter the holy places by the blood of Jesus" (Hebrews 10:19). Confession is directly to God (1 John 1:9); prayer directly to the Father; Scripture directly read and obeyed. No earthly priest mediates; Christ alone is the one Mediator (1 Timothy 2:5). This undoes the Roman sacramental system where the priest offers the Mass on behalf of the people. (2) Spiritual sacrifices. The NT redefines sacrifice: "present your bodies as a living sacrifice, holy and acceptable to God, which is your spiritual worship" (Romans 12:1); "through Him then let us continually offer up a sacrifice of praise to God... do not neglect to do good and to share" (Hebrews 13:15-16); "a fragrant offering, a sacrifice acceptable and pleasing to God" (Philippians 4:18, re: Philippian gift). Christian sacrifices are not the blood of animals but the lives, praise, and generosity of priests who have been redeemed. (3) Every believer in ministry. If every believer is a priest, every believer has a ministry. There is no "laity" in the Medieval sense of people who merely receive ministry from professionals. Certain offices exist (apostles, prophets, evangelists, pastor-teachers, elders, deacons), but they exist to equip the saints for their ministry (Ephesians 4:11-12). The whole body ministers. (4) Holy priesthood requires holiness. "Be holy, for I am holy" (1 Peter 1:15-16). The priest who offers dirty sacrifices dishonors God. Holiness is the lifestyle implication of the priestly identity.