I think that when people from modern protestant churches ask why we will not allow women to be priests what they are asking is why wonít we allow people to be ministers/pastors in our Church like they have ministers in their churches. Itís an innocent enough question and I donít think anyone means anything by it. But to answer the question I have to lay some groundwork; for starters the Catholic Church does not consider itself the same as other Christian Churches. The Church is here to teach, offer its members the Sacraments and continue the Sacrifice of the Mass until the end of time. We do not just read from the Bible hear some preaching, pray and then weíre done, we continue on to the Liturgy of the Eucharist where we believe Jesus becomes present under the appearance of bread and wine. All of the immediate descendents from the Catholic Church have kept their version of the Mass; the Orthodox churches kept their version of the Mass, the Lutheran Church has their version of the Mass and the Episcopal (Anglican) Church has kept their version of the Mass. Remember, this is the way all of Christianity worshipped God for 1500 years. Only as churches got further and further from their roots have they dropped and then forgotten about the Mass as a sacrifice.
If we look at the ancient Jews you will notice something different about them from all the other ancient religions on earth. Besides believing in only one God, the Jews only had male priests to offer sacrifice in the temple. There were no priestesses in Judaism. Every other religion has priestesses but the Jews never did. Our theology is that while the Jews offered animal sacrifice for the sins of the people, the Catholic Church offers the sacrifice of Jesus Christ in atonement of our sins and those of the whole world. It might sound strange if you are not Catholic but we offer God the Father the body and blood of the perfect and spotless sacrifice, our Lord Jesus Christ. We must have priests, just as the Jews had priests, to continue the re-presentation of The Sacrifice to God the Father.
Now, lest it sound like we self-appointed ourselves to carry out this work I want to emphasize the Church is just doing what Jesus demanded we do and we continue doing it. In John 6 Jesus calls Himself the bread of life and says that you have no life within you if you do not eat of it. How is that bread supposed to be made available to everyone throughout time? At the last supper He asked that we do this (the breaking of bread) in memory of Him. When He appeared on the road to His two Apostles they did not recognize Him, when they invited Him to eat with them He once again went through the ritual of breaking the bread then at once they knew who it was that was with them and He disappeared. (Luke 24:30-35) Again He shows that He wants us to keep practicing the communion ritual that became our Eucharistic (which means Thanksgiving in Greek) celebration, which we call the Mass. It is mentioned a couple of times in the Bible that thatís what the early Christian communities were practicing. So strong was the understanding that we were partaking in the Body and Blood that people outside of the Christian communities thought the Christians were practicing cannibalism.
Our priests must be male; there is no example of female priests in the Bible. I dare say it might be un-biblical to have anyone except a man functioning as priest in a church. If you read about the Korah rebellion in Numbers 16 you will see that God does not tolerate anyone who tries to act as a priest who has not been officially appointed. Not only does God kill all of those who would try to be priests but also the people who followed the renegade priests. So we take the office of priest very seriously. In Jude 11 it warns that those who usurp the office of the priesthood will be destroyed like those in the Korah rebellion. We will not have female priests and anyone within the Church who wants us to have female priests better get back to reading their Bible.