Article 2 of Question 2 is for the most part not a good point to stop and comment. St. Thomas offers an account of St. Augustine’s division of faith into credere Deo, credere Deum, and credere in Deum. As St. Thomas explains it, the first corresponds to the formal object of faith and the second to the material object of faith; we have looked at this distinction already. The third, he says, corresponds to the fact that in the act of faith the intellect is moved by the will, which urges on to God as a goal. This theme is something I want to save for a later point, because so much comes together around it.
But for the moment, I’ll just note that the distinction between credere Deo and credere Deum should be as much a playground for anyone interested in the Latin case system as it is a torment for anyone trying to translate the Summa into English. In general, the dative case (Deo) in Latin indicates a more spiritual object, as when I throw the ball to you, while the accusative case (Deum) indicates a more material object, as when I throw the ball at you. These line up reasonably well, I think, with the idea of formal and material objects.