The old formalisms of the law have become transformed into the new law.
1 In this way, then, one can discern in the individual sacraments the proper effect of each one and the becoming matter.
Now, first: Regarding the spiritual generation which takes place in baptism, one must consider that the generation of a living thing is a kind of change from non-living to life. But man in his origin was deprived of spiritual life by original sin, as was shown above; and still every single sin whatever which is added draws him away from life. Baptism, therefore, which is spiritual generation, had to have the power to take away both original sin and all the actual, committed sins.
2 Now, because the sensible sign of a sacrament must be harmonious with the representation of its spiritual effect, and since washing away filth in bodily things is done more easily and more commonly by water, baptism is, therefore, suitably conferred in water made holy by the Word of God.
3 And since the generation of one is the corruption of another, and since what is generated loses both its previous form and the properties consequent on that form; necessarily through baptism, which is a spiritual generation, not only are sins taken away, these are contrary to a spiritual life, but also every guilt of sins. For this reason, too, baptism not only washes away the fault, but also absolves from all guilt. Hence, no satisfaction for their sins is enjoined on the baptized.
4 Again, when by generation a thing acquires a form, it acquires at the same time the operation consequent on the form and the place in harmony with it. For fire, as soon as generated, tends upward as to its proper place. Accordingly, since baptism is a spiritual generation, the baptized are forthwith suited for spiritual actions, the reception of the other sacraments, for example, and other things of the sort, and forthwith there is due to them the place harmonious to the spiritual life, which is eternal beatitude. Hence, we say that “Baptism opens the gate of heaven.”
5 One should also consider that one thing has but one generation. Hence, since baptism is a spiritual generation, a man is to be baptized once only.
6 Clearly, also, the infection which entered the world through Adam makes a man guilty but once. Hence, baptism, which is chiefly ordered against this infection, should not be repeated. There is also this common consideration: that, as long as a thing is once consecrated, it must not be consecrated again, so long as it endures, lest the consecration appear inefficacious. And so, since baptism is a kind of consecration of the one baptized, baptism must not be repeated.
This excludes the error of the Donatists or Rebaptizers.