God had set apart one tribe in Israel (Exodus 32:26–29), and one family within that tribe (Exodus 28:1), to serve him as priests; that is, they would represent the people in approaching God in the tabernacle (think of sacrifices, prayer). Similarly, God had set apart one tribe in Israel for kingship (Genesis 49:10) and within that tribe one family (1 Samuel 16:1; 2 Samuel 7:13) to serve as king (represent God in governing his people).
Yet the Lord’s intent was that all the people should serve as priests and kings (Exodus 19:6), a reality that the priestly family and the kingly family were to foreshadow. Priests and kings in Israel were specially equipped by the Holy Spirit to carry out their task (1 Samuel 16:13). At Pentecost the Holy Spirit was poured out on all believers (Acts 2:4) so that all can function as priests and kings. Concretely, all believers have access to the King of kings, Jesus Christ, and may speak to this sovereign in prayer—a privilege not for those not born again.
Moreover, since God’s children are all living stones connected to Jesus Christ as the cornerstone (who is himself the sacrifice that paid for sin, 1 Peter 1:18, and so our “Lord,” 1 Peter 1:3), it follows that all God’s own share in his priesthood and kingship, and so need to be communally busy for the other’s benefit in holy service.
9 But you are a chosen race, a royal priesthood, a holy nation, a people for his own possession, that you may proclaim the excellencies of him who called you out of darkness into his marvelous light.