Saint Augustine on the Necessity of Baptism

In his first letter to Simplicianus, St. Augustine wrote against the Semi-Pelagians of his day:

The grace of faith precedes good works. The grace of faith is less in catechumens, more in the baptized. And first, I shall hold and consult the intention of the Apostle firmly expressed throughout the epistle. And this is so that no one should glory in the merits of works. The Israelites dared to glory that, because they had observed the law given to them, they merited the Evangelical grace. Hence they did not want that the same grace be given to the gentiles, being unworthy, unless they receive the Jewish sacraments. When this issue arose, it was settled in the Acts of the Apostles. They did not understand [that by the very fact] that Evangelical grace is not due to works, otherwise grace will no longer be grace [omit the part in brackets to understand it better. We would not say this normally in English]. He affirms this in many places, namely that the grace of faith precedes works, not to extinguish works, but to show that works do not precede grace but are its consequence, so that no one should consider that he had received grace because of his works, but that he cannot perform good works unless he had received grace through faith. Now man begins to receive grace when he begins to believe in God, being moved to faith by internal or external admonition. But we still need to know at what moment of time or by the celebration of the sacraments, grace is infused more plainly and evidently. For the catechumens do not lack faith. Or Cornelius, did he not believe in God when his almsdeeds and prayers proved him worthy to have an angel sent to him. Yet in no way would he have done these things unless he first believed, and in no way would he have believed unless he was called by admonitions, either secret, seen only of the mind, or open, manifest through the senses of the body. But the grace of faith in some is such that it is insufficient for obtaining the kingdom of heaven, as in the catechumens and in Cornelius himself before he was incorporated into the Church by receiving the sacraments; in others, the grace of faith is such as to make them the body of Christ and the holy temple of God. As the Apostle says: “know you not, that you are the holy temple of God” (1 Cor. 3:16); and also the Lord Himself: “Unless a man be born of water and the Holy Ghost, he will not enter into the kingdom of heaven.” Therefore the beginnings of faith have a certain similarity to conceptions, for in order to attain life eternal, it is not enough to be conceived, but one must be born. And none of these is without the grace of the mercy of God, because when works are good, they follow that grace, as was said, they do not precede it.