1. At the conclusion of the first question of the Summa, St. Thomas famously asks about the various senses of Scirpture. Nowadays when students are taught about the senses, they are taught St. Thomas's schema in abstract. It is worth noticing, however, that his presentation of these four senses emerges out of a good degree of controversy and confusion on what exactly the different senses are. For example, in the Sed contra he cites Gregory's Moralia, but the entire Moralia is structured on the use of three senses: historical, moral, and allegorical.
2. The content of the Corpus of this article is borrowed largely from Book I of St. Augustine's De Doctrina Christiana, where he explains a two-fold semiotics of scripture: that there words not only signify things, but those things in turn signify other, higher things. These different modes of signification open the door for the polysemic view of Holy Writ traditional in Christianity.
3. So, to summarize briefly: on the first level, the words of scripture signify a historical reality. "There was a man of the land of Uz whose name was Job." At times these words are meant not to convey the truth of the historical reality, but to employ the idea of the historical sense as a sign of something else. In this case, we can distinguish three main possibilities: first, the things described may convey a prophetic significance, foretelling the central event in the history of salvation: the Incarnation, Death and Resurrection of Christ. Second, they may convey a lesson on the right manner of living. Third, they may lead us to the understanding of divine, atemporal realities, the fulfillment of which we anticipate in the eschaton.
4. The other details of this article are worth looking over, but are also very easy to understand. This suffices for today's commentary. I will omit the usual outline.