Why can't women be ordained priests?

The teaching. "The Church has no authority whatsoever to confer priestly ordination on women, and this judgment is to be definitively held by all the Church's faithful" (St. John Paul II, Ordinatio Sacerdotalis 4, 1994; CCC 1577). The Congregation for the Doctrine of the Faith confirmed in 1995 that this belongs to the deposit of faith and is taught infallibly by the ordinary universal Magisterium.

Why. Jesus chose twelve men as apostles, freely and deliberately, in a culture where He broke conventions constantly: He spoke with the Samaritan woman, defended the adulteress, let women travel with Him and fund His ministry, and appeared first to Mary Magdalene. He gave His own Mother, the holiest human being who ever lived, no priestly role. The apostles did the same. The Church concludes that this was Christ's will, not cultural accident, and she is bound by it (CCC 1577).

The sacramental sign. The priest acts in persona Christi, in the person of Christ the Bridegroom, toward the Church, His Bride (Eph 5). The masculine sign is part of the sacrament's meaning, the way bread and wine (not rice and tea) are required for the Eucharist. Sacraments are not arbitrary; they use the signs Christ chose.

Not about worth. "The greatest in the kingdom of heaven" (Mt 18:4) is not a priest but whoever is most humble, and the Church's highest creature is a woman. Holiness, not office, is the measure. Women have led the Church as abbesses, foundresses, Doctors of the Church (Teresa, Catherine, Thérèse, Hildegard), theologians, and today as heads of Vatican departments. The priesthood is a specific sacramental role, not a promotion.

Deacons? The question of women deacons has been studied by two papal commissions without a definitive conclusion. The sacramental priesthood, however, is settled.