Theology may not be necessary for the salvation of an individual, but as a form of acquired wisdom, it is indispensable for those who are charged with instructing others (bishops and priests). While a Christian witness may lead others to Christ, in this providential order it is not sufficient for the conversion of all. A role has been given to some of us to lead others to Christ through words, and not just deeds.
The application of human reason to [understanding and relating] the truths of the faith can be considered theology. But if our ability to reason about Faith admits of different degrees of excellence, and can be perfected through an intellectual habit, then we should not reject outright the claim that theology is a science (as understood by Aristotle).