In both Old and New Testaments, there are three ranks of priests, which are commonly referred to as the high priests, the ministerial priests, and the universal priests.
At the time of the Exodus the high priest was Aaron (
Ex. 31:30), the ministerial priests were his four sons (
Ex. 28:21; the sons were Nadab, Abihu, Eleazar, and Ithamar, the first two of which were killed for abusing their priestly duties), and the universal priests were the people of Israel as a whole (
Exodus 19:6).
The three-fold model of the priesthood which was in use at the time of Aaron was carried over into the New Testament and thus we find there also a high priest, ministerial priests, and universal priests. In the New Testament age the high priest is Jesus Christ (
Heb. 3:1), the ministerial priests are Christ’s ordained ministers of the gospel (
Rom. 15:16), and the universal priests are the entire Christian people (
1 Peter. 2:5,
9).
So the Bible clearly states that all Christians are priests (
1 Peter 2:5,
9), as the Catholic Church clearly teaches for all who bother to read its teachings, see
Catechism of the Catholic Church 1141-4, 1268, 1305, 1535, 1547, 1591-2 on the common priesthood. But the Bible also said the same thing about the Israelites (
Ex. 19:6), yet this did not prevent there from being a separate, ministerial priesthood even before the Law of Moses was given (
Ex. 19:22,
24).
Furthermore, since the top, Old Testament office of high priest corresponds to Jesus, the New Testament high priest, and since the bottom, Old Testament universal priesthood corresponds to the New Testament universal priesthood, the middle, ministerial priesthood in the Old Testament corresponds to a middle, ministerial priesthood in the New Testament.
This priesthood is identical with the office of elder. In fact, the term “priest” is simply a shortened, English version of the Greek word for “elder” —
presbuteros — as any dictionary will confirm. This is any some Old Catholic translations render the word as “priests” where Protestant Bibles have “elder.” For example, in the Douay-Rheims Bible (the Catholic equivalent of the King James Version) we read:
“For this cause I left thee in Crete, that thou shouldst set in order the things that are wanting, and shouldst ordain priests in every city, as I also appointed thee” (Titus 1:5).
“Is any man sick among you? Let him bring in the priests of the Church, and let them pray over him, anointing him with oil, in the name of the Lord. And the prayer of faith shall save the sick man; and the Lord shall raise him up; and if he be in sins, they shall be forgiven him” (James 5:14-15).
We also see in the New Testament that the functions of the Old Testament elder — who served in the synagogue — have been fused with the functions of the Old Testament priest — whose served in the temple.
We can see the fusion of the two concepts in
Romans 15:15-16. In the New International Version of this passage, we read:
“I have written you quite boldly on some points, as if to remind you of them again, because of the grace God gave me to be a minister of Christ Jesus to the Gentiles with the priestly duty [literally, “the priestly work”] of proclaiming the gospel of God, so that the Gentiles might become an offering acceptable to God, sanctified by the Holy Spirit.”
Paul tells us that because he has been given a calling as a professional minister of Christ, he has a priestly work of preaching the gospel so that the Gentiles may be an offering — a sacrifice to God. This is not something only he has. Every elder in every church has that same “priestly work” of preaching the gospel. So Paul here conceives of the office of the New Testament minister as a priestly office. Notice that the hearers of the gospel in this passage are not depicted as priests, but as the sacrifice to God. Paul draws a distinction between himself and his work of preaching the gospel, and his readers and their duty of hearing it. It is the minister, not the congregation, who is here pictured as priest. The Office of New Testament Priest – Jimmy Akin
Titus 1:5
James 5:14-15
Romans 15:15-16