One of the disputed questions Aquinas deals with is: whether a child who is born in the desert where no water is available, and dies without baptism, can be saved in virtue of its mother's faith:
It seems that a child born in the desert can be saved without baptism in virtue of its parents' faith.
1.For faith in the time of grace is no less efficacious than in the time of natural law. But in the time of natural law children were saved in virtue of their parents' faith, as Gregory says. Therefore they also are so saved now in the time of grace.
2. Further, Christ did not constrict the way of salvation for men, since he says in John 10:10: "I came that they may have life, and have it more abundantly." But before the coming of Christ some children were saved in virtue of their parents' faith. Therefore much more are some thus saved after the coming of Christ.
But against this is what the Lord says in John 3:5, "Unless one is born of water and the Holy Spirit, he cannot enter the kingdom of heaven."
I respond, it should be said that no one can be freed from the damnation that the human race incurred on account of the sin of its first parent except through Christ, who alone is found immune from that damnation, that is, by being incorporated into him as a member to its head. Now this can take place in three ways.
First, by receiving baptism, according to Gal 3:27, "all you who have been baptized in Christ, have put on Christ." Secondly, by shedding one's blood for Christ, since by this someone is conformed to Christ's passion, from which baptism receives its efficacy; hence it is said about the martyrs in Rev 7:14, that "they have washed their robes etc… in the blood of the lamb." Thirdly, by faith and love, according to Prov 15:27, "by mercy and faith sins are cleansed," and Acts 15:9, "purifying their hearts by faith"; and by faith Christ dwells in our hearts, as is seen from Eph 3; hence also baptism itself is called the sacrament of faith.
Accordingly, there is said to be three kinds of baptism, namely of water, spirit, and blood; for the other two take the place of baptism of water, so long as there is the intention of receiving that baptism of water, so that it is a case of necessity, rather than religious contempt that excludes the sacrament.
Now it is manifest that there cannot be a motion of faith and love in children who do not yet have the use of reason, nor can there be the intention of receiving baptism; and therefore they cannot be saved except by the baptism of water, or by the baptism of blood if they are killed because of Christ, through which they not only are made Christians, but also martyrs, as Augustine says about the innocents.
Thus it is evident that the child who dies in the desert without baptism does not attain salvation.
To the first, therefore, it should be said according to some persons, in the time of natural law the parents motion of faith alone was not sufficient, but some external protestation of faith by some sensible sign was required. And on this view the only difference between what was then required and what is now required for salvation, is that now the sensible sign is determinate, while then it was indeterminate, and was up to the choice of the individual.
The opinion of others is that just the interior motion of faith in reference to the child's salvation sufficed for childrens' salvation. Yet the power of faith has not now been diminished, but the degree of salvation has been increased; for now those who are saved by Christ are immediately introduced into the kingdom of heaven, which before was not the case; hence it is not unfitting if something further is required for this, namely baptism, as is said in John 3:5.
To the second it should be said that Christ enlarged the way of salvation for men in that he opened to them the gates of eternal life, which before were closed by the sin of the first parent.