THOMAS MERTON was born 100 years ago tomorrow. Just as people remember where they were when President Kennedy was assassinated, I can recall with intense clarity the moment when I discovered Thomas Merton.

I was at the Sisterhood of St John the Divine in Toronto, several years ago, trying to decide whether God was calling me to become a nun, or whether I had totally misunderstood his instructions. It was a steamy summer afternoon, and my faith was wilting. Moping in the Sisterhood's guesthouse library, my eyes landed on Merton's autobiography, The Seven Storey Mountain.

His name had come up in conversations about religion's great and good, but I had assumed that he was just another boring, time-warped priest banging on about another "revolutionary" interpretation of the Gospels. Having nothing else to read at the time, I pulled The Seven Storey Mountain from the shelf, slumped in a chair, and opened the book.

Two pages in and you could not have prised it from my hands; five pages in, and I was frantically Googling "Merton" for his contact information. The crushing disappointment that I was 42 years too late is still palpable.

Anyone who has a passing acquaintance with Merton's prolific output will no doubt be taken aback by the milestone: Merton seems too modern, too "young" to be 100 years old. Read anything of his right now and you will be struck by its modernity, its confidence and muscularity. He wasn't afraid to throw a punch: academic, cultural, political, religious - Merton sparred with it. He loved God, but he was also critical of institutional religion. That endeared him to people back in the 1950s and '60s, and it resonates with people today. His famous prayer, with its mash-up of The Road Less Travelled and Psalm 23, taps into the Zeitgeist: "My Lord God, I have no idea where I am going./ I do not see the road ahead of me. . ."

I encountered varying attitudes to Merton from nuns and monks. One said that The Seven Storey Mountain had played a part in his decision to enter the religious life; another, when she saw Merton on my desk, groaned with barely disguised contempt. But the overwhelming majority were fans. Merton had an anti-Establishment cockiness that endears him to the quiet rebel angels in religious life.

When he died in 1968, tentative steps were taken to elevate Merton to sainthood. He was a pop star for the monastic set, abetted by the whiff of the messianic in his back story - bohemian artist parents (a New Zealander and an American), strangers in a foreign land (France) who were devoted to their son, and who gave him a free-range childhood (in the shadow of the Pyrenees). The story moves from tragedy to tragedy as the child morphs into a pampered misfit, a bewildered orphan, an arrogant toff, and then, like Saul, stumbles towards conversion.

The trajectory toward sainthood, however, sputtered, when a deluge of biographies and appreciations published after Merton's death stripped off his Vatican veneer: Fr Louis (as Merton was named in religion) proved to be rawer than was originally glimpsed. Merton hadn't come completely clean about his past in The Seven Storey Mountain. The drug use and promiscuity were well known but, after his death, there was the discovery of his part in a teenage pregnancy, and how his wealthy guardian had paid off the girl's family. The fact that the teenage mother and her infant son perished during the Blitz allows us better to understand the private torture that dogged Merton.

There was a further juicy revelation that, while still clothed in his Trappist habit, he had had a "gal on the side" and, at the time of his death, was considering leaving his beloved Gesthemani. Yet, how are any of these falls from grace different from the recently canonised Angela of Foligno, the 13th-century good-time girl who whored her way through life, until she repented of her behaviour, and founded a religious order?

Like almost every saint, Merton possessed a complex personality: his unmonk-like hubris versus his humility; his pining for freedom from his monastic vows versus his determination to stick to them; his desire for peace and quiet versus his penchant for sneaking out of the monastery to drink, and mingle in the local bars with secular folk.

Merton was the contemplative contradiction, and this makes him deliciously relevant and accessible. Merton's writing stimulates and edifies, and has much to offer the current conversation about revisioning the Church. His centenary is a perfect opportunity to introduce this imperfect monk-priest to a new generation.

Jane Christmas is the author of And Then There Were Nuns (Lion Hudson).