Your step-mother may not understand the theology behind the Catholic priesthood, it sounds like to me. I would second the Dr. Pitre endorsement.
Even Protestants believe there is a NT priesthood, which they call the priesthood of believers. (
But you are a chosen race, a royal priesthood, a holy nation, God’s own people 1 Pet. 2:9) Catholics also teach this doctrine (e.g.
CCC#1174).
Regarding the ministerial priesthood, that’s a different issue. Catholics also believe there is one priest. However, all “priests” participate in Christ’s ONE priesthood.
CCC#1545 The redemptive sacrifice of Christ is unique, accomplished once for all; yet it is made present in the Eucharistic sacrifice of the Church. The same is true of the one priesthood of Christ; it is made present through the ministerial priesthood without diminishing the uniqueness of Christ’s priesthood: "
Only Christ is the true priest, the others being only his ministers."So you see, your step-mother’s argument does not apply to Catholic teaching, because we essentially do not believe there is more than one NT priest.
Once one begins to understand that Christ perpetuates his priesthood sacramentally through his ordained ministers, one can make sense of such passages like this one in Hebrews:
Hebrews 13:10 We have an altar from which those who serve the tent have no right to eat. For the bodies of those animals whose blood is brought into the sanctuary by the high priest as a sacrifice for sin are burned outside the camp. Your step-mother may not realize this, but an “altar” Biblically is a place for sacrifice. You can see the comparison even in the short passage above when the NT altar is compared to the OT sacrifices. Where the OT ate the slaughtered animal, we Catholics in the NT actualize the fulfillment of those sacrifices by eating the bread - which is Christ’s sacrifice (e.g.
Luk. 22:19,
1 Cor. 10:16, etc.)
For further reference, I recommend:
The Ministerial Priesthood