Thomas Aquinas's work was influenced by his engagement with Aristotle. Aquinas found Aristotle's logic and methods of reasoning persuasive, and he wanted to demonstrate that such principles were not incompatible with Christian faith. Aquinas's respect for human reason is evident in his understanding of natural law, which has influenced the way we think about law in the West ever since.
Aquinas posited the natural law as a series of precepts, such as "good is to be encouraged and evil avoided" and "what is done to preserve life is generally good." He believed humans would apply their natural reason to these precepts in order to generate the human laws that governed their communities.
There are two key implications in Aquinas's work: first, that reason is not hostile to faith, and second, that human activities on earth—like law and governance—are worth pursuing well and can be a reflection of God's glory.
The spirit of intellectual curiosity and desire to engage with the world continue to be reflected in various Catholic orders and in the daily lives of laypeople.
Augustine, on the other hand, is usually considered a Neoplatonist because of his interest in the Ideal, an interest Plato also shared. Thus, Augustine also sees a place for reason alongside faith. However, unlike Aquinas, Augustine is more skeptical about humans using their reason to create things here on earth.
For Augustine, the Ideal can only be attained in the eternal kingdom of Heaven, because in Heaven there is only proper Christian love, caritas. On earth, we must deal with many obstacles, distractions, and burdens that threaten to replace our craving for caritas with a craving for earthly goods (Augustine called that craving cupiditas).
Indeed, it is possible to read Augustine as suggesting that using our reason to focus too narrowly on the law, government, or even certain types of cultural activities is, in some senses, a waste of our time, and that we should instead live more contemplative lives. This reading of Augustine leans heavily on his autobiography, the Confessions. Augustine's engagement with these questions of contemplation and craving have drawn modern philosophers who are interested in existentialism to his work. For example, Hannah Arendt wrote her dissertation on Augustine's work.