“I am sure it was not a mere accident that the primitive Church did not apply the term ιερευς (hiereus, “priest”) to either bishop or presbyter. It was applied in the first place to Christ: He is the priest, the high-priest eternal. The whole Epistle to the Hebrews deals with this subject. Then in the second place, they applied the term to the assembly of Christians in so far as they are associated with Christ and can glorify God with Him and through Him. And it was only in the third instance that the term was also applied to bishops and priests, that the words ιερευς and sacerdos [“priest”] were used of Christian ministers of the altar; for the επισκοπος [episkopos] and πρεσβυτερος [presbyteros] of the new order of salvation occupied an altogether different position from that of the pagan priest or even the priest of the Old Testament.
Among the pagans and even in the Old Testament, the ιερευς was someone who himself, in his own name or at the command of the community, acted as mediator with the deity. Such a possibility does not exist in the New Covenant. For there is only one mediator between God and man, Jesus Christ, and all others are merely His instruments, able to act not in their own name but only His. The term ιερευς was therefore applicable only to Christ and to the whole communion of the faithful, the holy Church, in so far as it is joined to Christ.”
-From The Early Liturgy: To the Time of Gregory the Great, by Josef A. Jungmann, S.J., 1959.
The Pantheon, built (and partially designed by the emperor Hadrian) as the temple to all the gods, later consecrated as a church to Santa Maria ad Martyres