Quoting Hilary, Kelly explains how it is belief rather than unbelief that is true wisdom:
Thus all unbelief is foolishness, for it takes such wisdom as its own finite perception can attain, and measuring infinity by that petty scale, concludes that what it cannot understand must be impossible. Unbelief is the result of incapacity engaged in argument. Men are sure that an event never happened, because they have made up their minds that it could not happen. (De Tinitate, III.24 p.19