Note: Below is my answer to a question on Quora, Why are there no female Roman Catholic priests?, republished here for posterity.
Before answering the specific question above, I'd like to give a few quick introductory notes:
- The Catholic Church has, throughout history, been the first to support the plight of the poor, the freedom of religion for all peoples, and a 'preferential option for the poor'. To say the Church goes against the poor in disciplining (helping correct faults) orders of religious who have done things against the faith (often blatantly so) and against the Church is a logical fallacy. The Church supports and upholds the poor and those who serve them—but they do not condone doing so while also causing scandal and spreading falsehoods that lead people astray.
- The doctrine and fundamental teachings of the Church are not decided through a democratic process, nor can they be changed. Certain applications of this teaching (e.g. such as what makes a 'just war' and the morality of capital punishment) can and do change with location and time, but the core doctrine (e.g. 'thou shalt not kill') never changes.
- There is evidence in both the Bible and in the earliest writings of the saints that there were never any female priests. There were (and are!) women who played active roles in the Church, as prophets, intercessors, and even doctors of the faith. But there were never any women who acted in persona Christi (in the person of Christ) and conferred the Sacraments of Holy Orders, the Eucharist, Confirmation, Reconciliation, or Anointing of the Sick.
The simplest, most obvious reason women cannot be ordained priests is that a priest does not act on his own when he performs sacred acts like calling down the Holy Spirit to turn the bread and wine offered at Mass into Jesus' body and blood. He acts in persona Christi ('in the person of Christ'). This is not play-acting; this is the priest, mysteriously acting as Christ himself (who chose to become incarnate as a human male), in the performance of a sacred act. Just as water cannot be transformed into Jesus' blood (only wine may be used), a woman cannot act in persona Christi.
This is not so because Jesus/the Church/the heirarchy/the Pope hates women or is sexist. On the contrary, it is simply the way things are. Just as a man cannot conceive a child within him, a woman cannot act in persona Christi, because she is not male. Some see this as sexist, but that's really a problem of perspective.
Finally the question of whether the Church will ever allow women to be ordained priests is a question which has been answered time and time again, always with a simple "No." And yet it is still asked...
"Although the teaching that priestly ordination is to be reserved to men alone has been preserved by the constant and universal tradition of the Church and firmly taught by the magisterium in its more recent documents, at the present time in some places it is nonetheless considered still open to debate, or the Church’s judgment that women are not to be admitted to ordination is considered to have a merely disciplinary force. Wherefore, in order that all doubt may be removed regarding a matter of great importance, a matter which pertains to the Church’s divine constitution itself, in virtue of my ministry of confirming the brethren (cf. Luke 22:32) I declare that the Church has no authority whatsoever to confer priestly ordination on women and that this judgment is to be definitively held by all the Church’s faithful"
(Pope John Paul II, Ordinatio Sacerdotalis 4).
"[This teaching] requires definitive assent, since, founded on the written Word of God, and from the beginning constantly preserved and applied in the tradition of the Church, it has been set forth infallibly by the ordinary and universal magisterium (cf. Second Vatican Council, Dogmatic Constitution on the Church, Lumen Gentium 25:2)"
(Oct. 25, 1995 response by the Congregation for the Doctrine of the Faith).
None of this precludes women from having roles of administrative and/or other forms of authority in the Church, nor does it in any way diminish the incredible contributions of faithful women around the world in all they do for the faith. Indeed, there are so many examples of holy women who do so much for our Church—without denying basic tenets of the faith—that I dare anyone to compare a modern nun (who sees it her duty in life to oppose Catholic bishops) favorably against the likes of Mother Theresa, St. Thérèse of Liseaux, St. Joan of Arc, St. Catherine of Siena, or St. Teresa of Avila, or St. Gianna.