There is now, I think, wanting in these remarks no answer to inquiries concerning the Gospel mystery, except that on Faith; which we give briefly in the present treatise. For those who require a more elaborate account we have already published it in other works of ours, in which we have explained the subject with all the earnestness and accuracy in our power. In those treatises we have both fought controversially with our opponents, and also have taken private consultation with ourselves as to the questions which have been brought against us. But in the present discussion we have thought it as well only to say just so much on the subject of faith as is involved in the language of the Gospel, namely, that one who is begotten by the spiritual regeneration may know who it is that begets him, and what sort of creature he becomes. For it is only this form of generation which has in it the power to become what it chooses to be.
Source: The Great Catechism (New Advent)