Chapter I.
On those seven topics with which theology deals, in summary.
In the beginning it must be understood that sacred doctrine, namely theology, which principally treats of the first principle, that is, of God three and one, treats of seven topics in all, namely: first, of the Trinity of God; second, of the creature of the world; third, of the corruption of sin; fourth, of the Incarnation of the Word; fifth, of the grace of the Holy Spirit; sixth, of sacramental medicine; and seventh, of the state of the final judgment.
The reason for this truth is as follows: since sacred Scripture, or theology, is a science giving sufficient knowledge of the first principle according to the state of the wayfarer, insofar as is necessary for salvation; and since God is not only the principle of things and the effective exemplar in creation, but also the restorative in redemption and the perfective in retribution: therefore it treats not only of God the Creator, but also of creation and creature. And because the rational creature, which is in a certain way the end of all things, did not stand firm, but by its fall needed to be restored, therefore it treats of the corruption of sin, the physician, health, and medicine, and finally of the perfect cure, which will be in glory, with the impious cast into punishment.
And therefore it alone is a perfect science, because it begins from the first, which is the first principle, and arrives at the last, which is the eternal reward; it begins from the highest, which is God most high, the creator of all things, and arrives at the lowest, which is the punishment of hell.
It alone is also a perfect wisdom, which begins from the supreme cause, as it is the principle of things caused, where philosophical knowledge terminates; and passes through it, as it is the remedy of sins; and leads back to it, as it is the reward of merits and the end of desires. And in this knowledge is perfect savor, life, and the salvation of souls; and therefore the desire of all Christians ought to be inflamed to learn it. From these things it is clear that although theology treats of so many and such varied matters, it is nevertheless one science, whose subject, as that from which all things come, is God; as that through which all things come, Christ; as that to which all things tend, the work of restoration; as that around which all things center, the unique bond of charity, by which heavenly and earthly things are connected; as that about which all things contained in the canonical books treat, the credible as credible; as that about which all things in the books of the expositors treat, the credible as intelligible, according to Augustine in On the Usefulness of Believing, for "what we believe, we owe to authority; what we understand, we owe to reason."