Drawing from an earlier Vatican document, "Declaration Inter Insigniores on the question of the Admission of Women to the Ministerial Priesthood" issued by the Congregation for the Doctrine of the Faith in October 1976, Pope John Paul explains the official Roman Catholic understanding that the priesthood is a special role specially set out by Jesus when he chose a dozen men out of his group of male and female followers. Pope John Paul notes that Jesus chose the Twelve (cf. Mk 3:13-14; Jn 6:70) after a night in prayer (cf. Lk 6:12) and that the Apostles themselves were careful in the choice of their successors. The priesthood is "specifically and intimately associated in the mission of the Incarnate Word himself (cf. Mt 10:1, 7-8; 28:16-20; Mk 3:13-16; 16:14-15)".
The letter concludes with the words: 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 Our ministry of confirming the brethren (cf. Lk 22:32) We 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. (Declaramus Ecclesiam facultatem nullatenus habere ordinationem sacerdotalem mulieribus conferendi, hancque sententiam ab omnibus Ecclesiae fidelibus esse definitive tenendam.)
Ordinatio Sacerdotalis was not issued under the extraordinary papal magisterium as an ex cathedra statement, and so is not considered infallible in itself. Its contents are, however, considered infallible under the ordinary magisterium, as this doctrine has been held consistently by the Church. In a responsum ad dubium (reply to a doubt) explicitly approved by Pope John Paul II and dated October 1995, the Congregation for the Doctrine of the Faith stated that the teaching of Ordinatio Sacerdotalis had been "set forth infallibly by the ordinary and universal Magisterium" and accordingly was "to be held definitively, as belonging to the deposit of faith".
In 1998, this was clarified slightly (in the Congregation for the Doctrine of the Faith's Doctrinal Commentary on Ad Tuendam Fidem) to state that the teaching of Ordinatio Sacerdotalis was not taught as being divinely revealed, although it might someday be so taught in the future:
A similar process can be observed in the more recent teaching regarding the doctrine that priestly ordination is reserved only to men. The Supreme Pontiff, while not wishing to proceed to a dogmatic definition, intended to reaffirm that this doctrine is to be held definitively, since, founded on the written Word of God, constantly preserved and applied in the Tradition of the Church, it has been set forth infallibly by the ordinary and universal Magisterium. As the prior example illustrates, this does not foreclose the possibility that, in the future, the consciousness of the Church might progress to the point where this teaching could be defined as a doctrine to be believed as divinely revealed.