Articles 3 and 4 of Question 2 address the necessity of faith in general. Just to drive home the connection between these questions on faith and the definition of theology, I want to point out the parallel between what St. Thomas does here and what he does in ST I.1.1 on theology.
In that first article of the entire Summa, St. Thomas asks whether it is necessary to have “Sacred Doctrine,” which he later refers to by the name “theology.” He responds that it is necessary because we are ordered an end above our nature, and so we need more than reason can provide, and even we regard to what reason can know about God it was necessary that such knowledge be known more commonly, more quickly, and without error.
In ST II-II.2.3, St. Thomas argues that faith is necessary because we are ordered to an end above our nature. In ST II-II.2.4, he then argues that faith is necessary even with regard to things knowable by reason because that knowledge needs to be gain more quickly, more commonly, and with more certitude than reason offers. In other words, he gives all the same arguments but in more detail.
So here’s the punchline, according to St. Thomas: the reason we need to have theology is the same reason we need faith itself.
