1. Thomas's first quaestio is a methodological one: What is the nature and extent of sacred doctrine (sacra doctrina)? He begins this question by asking whether we need such a thing as "sacra doctrina." Isn't Philosophy good enough to supply any knowledge we might need?
2. The objections are both interesting. First, he quotes Sirach, "seek not the things that are too high for thee." In other words, Philosophy extends to the natural limits of human knowledge, and anything which transcends those limits is not appropriate for humans to know. It is pride to seek an excellence that exceeds one's proper place.
3. Second, he points out that knowledge has to do with being, i.e. what exists, because only the truth can be known, and there is only truth concerning what exists. And since philosophy (which is divided into various sciences: physics, ethics, politics, biology, psychology, metaphysics, etc.) studies everything that exists, including God, there's no need for anything else.
4. For the Sed Contra, he quotes Paul to the effect that all Scripture is profitable for teaching, reproving, etc. Since scripture is not part of philosophy, but divinely revealed, there must be some knowledge that is useful outside of philosophy.
5. In the Corpus of the article, St. Thomas gives two reasons for the necessity of sacra doctrina. First, that man is ordered by God to a supernatural end, a supernatural communion with God, which he cannot orient himself toward without knowledge, since the act of the will in desiring follows the act of the intellect in recognizing. Hence, since natural knowledge is insufficient to lead us to this supernatural end, it was fitting that God reveal himself to us supernaturally, by means of divine revelation.
6. Second, because even those things concerning God which can be known by reason (e.g. his existence, infinity, perfection, etc.) are known only with great effort, after a lot of study, and with "the admixture of many errors". In other words, though we can know that God exists with certainty through natural reason (cf. Vatican I constitution Dei Filius), still on account of the weakness of the intellect, that knowledge is very difficult to come by in a philosophically rigorous way.
7. In response to the quotation from Sirach, St. Thomas points out the next verse, "many things are shown to thee above the understanding of man." It would be prideful for man to demand what was beyond him, but once it has been freely offered it is fitting for him to accept it in faith.
8. In response to the second objection, St. Thomas makes an important point about the division of the sciences. He says that sciences are distinguished from each other by the manner through which their knowledge is acquired. Each science abstracts from its object by considering it only under a particular aspect, and all the natural sciences conern themselves with material being and its properties. Natural theology, which is a division of philosophy, develops a picture of God based on inferences from the character of the material world (aka "the way of remotion") to its immaterial creator. Revealed theology, on the other hand, develops a picture of God based on the data of divine revelation.
An outline of the article:
Objections: There should not be any doctrine beyond philosophy, because:
-Man ought not to seek what is beyond his nature.
-Philosophy leaves no room for another science.
Corpus: Sacred doctrine is necessary for salvation, because:
-Supernatural knowledge is required for us to be oriented to our supernatural end.
-Even natural knowledge of God, apart from revelation, is very difficult to come by.
-It is not wrong to accept a gift, even if that gift were beyond one's capacity to attain for oneself.
-The principles of philosophical theology and revealed theology differ: one is remotion from material being, the other is supernaturally revealed truth.