I think there should be a "Bad Theology" column, along the lines of Ben Goldacre's "Bad Science" column in the Guardian. There would be no shortage of candidates and, while some atheists would qualify, so would many theologians. But to refer to bad theology implies that there's also good theology – a suggestion which would be ridiculed by those who regard all theology as being on a par with studying tooth fairies and orbiting teapots. So what is good theology?

The response to that question would depend on who you ask. The word "theology" comes from the Greek theos and logos, which could be translated as reasoning about God. Although there are Jewish, Muslim and other non-Christian theologies, I write as a Catholic theologian with a feminist bias. (John Ruskin described the study of theology as a "dangerous science" for women).

Sometimes, debates between theologians and scientists give the impression that God is a being who can be spoken of objectively like any other being. To borrow a phrase from philosopher Grace Jantzen, they speak as if God is "an infinitely extended (and disembodied) version of an Oxford professor" who may or may not exist. But as good theologians know, the word "God" does not refer to anything that the human mind can comprehend, so theological language has at its heart an all-pervasive mystery which haunts human consciousness. The task of theology is like Penelope weaving her shroud – what we weave during the day we must unravel by night. That is why theology is derided by those who insist that all claims to knowledge must be rooted in rationality and factual evidence.

Classical theology understands God not as a being but as the very condition of all being, so that the word "being" is better understood as a verb than a noun. "The being of God is the doing of the world", to quote one theologian writing about Thomas Aquinas. Good theology approaches the question of God not as this or that being, but as the continuous activity of creating and sustaining all being, as the redeemer of creation from within through the incarnation of Jesus Christ, and as the revealing love of the holy spirit. To speak of the existence of God in this sense is more like speaking of the existence of love or beauty than of mountains or daffodils. We say that love exists, not only because it affects our world but also because we look for evidence of its existence in the ways in which people who use that word behave towards one another. Good theology involves doing as well as thinking, for the theologian must give material expression to her use of the word "God" in a way that counts as meaningful.

Theology is at its best when it works in a triangular relationship with scripture, creation and culture, continuously asking how the texts and traditions of the Christian faith are to be interpreted in the light of the questions of our time. According to the classic doctrine of grace, articulated by Aquinas, "grace perfects nature", so that there is no inherent contradiction between faith and reason, theology and science. Good theology serves as an intellectual rudder which steers faith along the narrow pathway between tradition and transformation, mystery and knowledge, contemplation and action, always seeking to bring the claims of revelation into creative dialogue with the discoveries of science and other forms of human understanding.

But theology also belongs within the secular study of the history of ideas, since it has had a formative influence in the making of the western world in its beliefs and values and its forms of artistic and cultural expression. To deny theology's historical significance is to succumb to the anti-intellectualism of a rigid secularist ideology which infects many modern universities. Those who lack any theological education simply do not have the resources for a meaningful engagement with much of western history and culture.

The refusal to allow theology a place in the university also plays into the hands of religious extremists, for it suggests that religion is only for the ignorant and the credulous, leaving vast numbers of the world's people at the mercy of bigots, tyrants and madmen. To do theology well is to empower people to resist religion's co-option by the powers of fanaticism and violence, and that is why the theological education of women is particularly important. John Ruskin was right – it is dangerous for women to study theology, not for women themselves but for a male theological elite which continues to exercise power in the name of a God it seeks to control. Good theology challenges claims to knowledge of God which refuse to engage with the demands of justice and reason, providing reason is understood not in the narrow terms of scientific rationalism but more broadly as the ability to give a coherent account of what one believes and why.

Finally, theology is concerned with questions about the conditions under which science is possible at all: why is there something rather than nothing, and why is that something intelligible to human consciousness? To ask such questions is human. To answer them may be divine.