Happenby: The Church's teaching on baptism is not dependent on fallible theologians or saints, but on the infallible magisterium, the popes, and without doubt, the Council of Trent. "If anyone says that true and natural water is not necessary for baptism and thus twists into some metaphor the words of our Lord Jesus Christ: 'Unless a man be born again of water and the Holy Ghost, let him be anathema."
Reply: All the canon you quoted means is that the sacrament of baptism requires real water, and that the “water” spoken of by Our Lord cannot be understood metaphorically.
The separate question of whether a person can obtain the salvific effects of baptism – i.e., translation into the state of justification by the infusion of sanctifying grace – without receiving the sacrament in re, is treated in another place.
When discussing the sacraments in general, the same Holy Council teaches:
CANON IV.”If any one saith, that the sacraments of the New Law are not necessary unto salvation, but superfluous; and that, without them, or without the desire thereof, men obtain of God, through faith alone, the grace of justification;-though all (the sacraments) are not indeed necessary for every individual; let him be anathema.
It goes on to explain that the salvific effects of the Eucharist, Penance, and Baptism can be obtained by desire. Concerning baptism, we read:
"And this translation (to the state of justification), since the promulgation of the Gospel, cannot be effected, without the laver of regeneration, at least in the desire thereof, as it is written; “unless a man be born again of water and the Holy Ghost, he cannot enter into the Kingdom of God.”
The above teaching has always been understood as meaning the desire for baptism can suffice for salvation, provided that the person makes a supernatural act of faith combined with a perfect act of charity. Two quotations will suffice, both of which are from doctors of the Church:
Bellarmine: “But without doubt it must be believed that true conversion supplies for Baptism of water when one dies without Baptism of water, not out of contempt, but out of necessity… For it is expressly said in Ezechiel: If the wicked shall do penance from his sins, I will no more remember his iniquities... … Thus also the Council of Trent, Session 6, Chapter 4, says that Baptism is necessary in fact or in desire.
St. Alphonsus: “But baptism of desire is perfect conversion to God by contrition or love of God above all things accompanied by an explicit or implicit desire for true Baptism of water, the place of which it takes as to the remission of guilt, but not as to the impression of the character or as to the removal of all debt of punishment. … Now it is de fide that men are also saved by Baptism of desire, by virtue of the Canon Apostolicam De Presbytero Non Baptizato and the Council of Trent, Session 6, Chapter 4, where it is said that no one can be saved “without the laver of regeneration or the desire for it.”
Just as a baptized person in mortal sin can obtain the salvific effects of Penance (infusion of grace and remission of sin) by means of an act of perfect contrition, so too can one obtain the salvific effects of baptism by a perfect of contrition combined with supernatural faith.
In condemning the errors of Fr. Feeney, the Holy Office wrote:
“In His infinite mercy God has willed that the effects, necessary for one to be saved, of those helps to salvation which are directed toward man's final end, not by intrinsic necessity, but only by divine institution, can also be obtained in certain circuмstances when those helps are used only in desire and longing. This we see clearly stated in the Sacred Council of Trent, both in reference to the sacrament of regeneration [i.e. baptism] and in reference to the sacrament of penance.”
Here we have the Magisterium itself interpreting the above citation from Trent as teaching that the salvific effects of baptism can be obtain by “desire and longing”. This is not merely the teaching of a theologian, or even of a doctor of the Church, but of the Magisterium.
Many more quotations could be provided, but these should suffice for any Catholic of good will.