The enigmatic, iconic theologian Søren Kierkegaard was born on this day. He was a divisive thinker who challenged the nominal Christianity of his day with the power of a radical, life-changing gospel.

Kierkegaard was born on 5 May 1813 in Copenhagen, Denmark. He grew up in a world where everyone was supposedly a Christian; under the dominant Lutheran state church, Christianity was simply part of what it meant to be Danish.

Kierkegaard's aim was to 'reintroduce Christianity to Christendom', showing people that true faith was a radical step, a choice between Christ and the world, with a personal, challenging relationship with God at its core.

This poet's provocative philosophy didn't make him many friends in his day, but he went on to inspire modern heroes of the faith such as Bonhoeffer, Karl Barth and Martin Luther King Jr. For those thinkers, Kierkegaard showed how true Christianity could never collapse into nominal nationalism.

Many of the Dane's thoughts and phrases have entered the modern English language. As biographer Stephen Backhouse notes, idioms such as 'walking the talk', 'mob rule' and the 'leap of faith' all go back to Søren. Here are nine quotes to remember him by.

1. The invitation stands at the crossroad...come here, you are so close to [Christ]; one single step onto the other way and you are so infinitely far away from him...oh, turn around and come here, here is rest!

2. The truth is a snare: you cannot have it, without being caught. You cannot have the truth in such a way that you catch it, but only in such a way that it catches you.

3. Although an outsider, I have at least understood this much, that the only unforgivable high treason against Christianity is the single individual's taking his relation to it for granted.

4. The highest and most beautiful things in life are not to be heard about, nor read about, nor seen but, if one will, are to be lived.

5. Prayer does not change God, but it changes him who prays.

6. What matters is to find my purpose, to see what it really is that God wills that I shall do; the crucial thing is to find a truth for me, to find the idea for which I am willing to live and die.

7. The public is all and nothing, the most dangerous of all powers and the most meaningless.

8. God creates out of nothing. Wonderful you say. Yes, to be sure, but he does what is still more wonderful: he makes saints out of sinners.

9. The tyrant dies and his rule is over, the martyr dies and his rule begins.