I wrote this a while back concerning the “authority” of the ordinance of baptism, and it addresses the GC “expanding its reach beyond the nation of Israel as well:
Starting with the main passages that support the POAB, 1Peter 2:9-10, we are told about individuals being a royal priesthood and as princes and priest have been consecrated to God while being told we are priest in a higher sense than the Jews. That is significant because it refers to the OT priests who were chosen by God, not self-appointed, to serve Him by offering up spiritual sacrifices.
This refers to the temple veil that only they were to pass which was torn in two by God upon Jesus’ death. It indicates the OT priesthood was no longer necessary and now believers could go directly to God through the High Priest, Jesus Christ. All this points to that as believers we have been given a freedom from the OT ways pertaining to that type priesthood:
(Hebrews 4:14) Seeing then that we have a great high priest, that is passed into the heavens, Jesus the Son of God, let us hold fast our profession.
(Hebrews 4:15) For we have not a high priest which cannot be touched with the feeling of our infirmities; but was in all points tempted like as we are, yet without sin.
(Hebrews 4:16) Let us therefore come boldly unto the throne of grace, that we may obtain mercy, and find grace to help in time of need.
We no longer have earthly mediators between God and man as existed in the OT:
(1 Timothy 2:5) For there is one God, and one mediator between God and men, the man Christ Jesus;
Now for those quotes:
"All Christians are priests, and all priests are Christians. Worthy of anathema is any assertion that a priest is anything else than a Christian."~ Luther
“John Calvin applied that message by forming a polity wherein laity and clergy alike would serve in ordained offices of leadership—as peers in proclamation of the Word, peers in intercessory prayer, and peers in mission service.”