Isaiah 61 says, "you shall be called the priests of the LORD; they shall speak of you as the ministers of our God..." (Isa 61:6). This is the case for us through faith in Jesus because Jesus acted as a priest during His life among us, as a priest for the offering of His sacrifice on the cross, and continues to act as a priest by interceding for us even today. He has made us priests who serve God and serve others. Intercessory prayer is a good example -- you are serving God by praying and serving others by taking their needs to God. Thus you do not stop being priests when you leave worship on Sunday morning but continue to lead in worship everywhere you go when you intercede for those in need, bind up the brokenhearted and injured, interpret and teach the Scriptures, and etc. As priests you are ministers of mercy to those in misery. Everyone is a priest, whether bowing down before idols or worshiping the true and living God, but thanks be to God if through faith you have become true priests of the LORD to the world.