His fictions depict characters who could do nothing but what their being drove them towards. "The Circular Ruins" enclose one man driven on a quest to dream another man, dream him whole, and set him free on the earth. We find at the end that his motive is set because, without his knowing, he himself was dreamed by another. "Death and the Compass" follows a detective whose investigation of a spree of murders both drives and solves the spree - he himself is both questioner and answerer, or perhaps just question and answer. "The Theologians" watches two mediaeval monks, opponents and competitors in doctrinal study, who over the course of their work establish themselves as symmetric: the neither would exist, in current form, without the other. Each was himself in order that the other could be himself.
Some of his fictions are not character driven, but they are nonetheless imbued with a driving pattern. "Pierre Menard, Author of the Quixote" asks a question of the world: if all fiction had to have been written. "Lottery of Babylon" is a chronology of a lottery that grows to encompass nonmonetary, and eventually ecclesiastical, powers; in eventuality it becomes a religion whose one heresy is that all chance is not planned in advance by the secret Company which runs the lottery.
His poetry, and essays on history and literature are more complex and open-ended, set as they are in a less mutable world. But again we see Borges reach into the scene and trace a structure, a connection; a connection much more suprising and perverse than any found in a survey history text. (and has not all brilliance some element of perversity?)
I am intentionally simplifying Borges' works. Each of his stories has much more interesting, unique concepts, simply couched in the framework I have described above. I know that none of this is literally relevant to our lives. We have total choice in our dealings, we can be anything we want. But we have choice in interpretation, and a world of mathematic description, one whose past, present, and future come together in a cohesive whole, is intensely useful in the infinite Now, where we construct these patterns to give motive to our daily activities.