Forty years ago today, Thomas Merton, a Trappist monk and perhaps the most popular American Catholic writer in history, stepped out of a bathroom shower during a visit to Bangkok. Slipping on the wet floor, he grabbed a poorly wired fan for support and was electrocuted. For many years, Merton had unsuccessfully sought permission from his superiors to travel outside his monastery in Bardstown, Kentucky. A few months after a new abbot was elected in early 1968, he assented to Merton’s request to attend an interfaith conference that December in Thailand. En route he met the Dalai Lama, who called him a “Catholic geshe,” or spiritual master.

Merton enjoyed paradoxes, and spoke of himself, like Jonah in the whale, as living in the “belly of a paradox.” The author of “The Seven Storey Mountain,” an autobiography that became an instant bestseller upon its publication in 1948, was a humble man who enjoyed fame, a Catholic priest fascinated by Zen Buddhism, a solitary mystic who craved company, and a cloistered monk who died far from home.

Paradoxes characterize Merton’s legacy as well. Why is this devout Catholic writer, whose autobiography proclaims a triumphal view of Catholicism and faintly mocks other religions, so beloved by seekers, doubters and agnostics? Conversely, why is this Catholic priest rejected in so many contemporary Catholic quarters?

The first paradox is explained by his writings. Merton’s most popular works are not the heavy-going theological tomes, but his autobiographical writings and journals. By turns lively, chatty and profound, Merton struggles with prayer, grumbles over his abbot’s refusal to let him travel, and fumes about being silenced by the Trappists when he writes about peace during the Cold War. Near the end of his life, he falls in love with a nurse he meets during a hospital stay. In all these experiences, he seeks to see signs of God.

Merton appeals to seekers and doubters because of his unflinching honesty in his quest for the “true self” and for God. No matter how long he has been a monk, Merton considers himself en route to God. (His most famous prayer begins, “My Lord God, I have no idea where I am going.”) And he is not afraid to change his mind, later rejecting the more solipsistic passages in his autobiography. “The man who finished ‘The Seven Storey Mountain’ … is dead,” he wrote in 1951. He is open, transparent, curious, protean and, finally, human.

His appeal among Catholics, however, is not as solid. In 2005, the editors of the “United States Catholic Catechism for Adults” planned to feature stories of prominent American Catholics. Initially, Merton was included among other noteworthies, until some high-profile Catholics opposed the move. Bowing to pressure, the editors expunged him. One bishop explained that Merton no longer speaks to contemporary readers, a surprise considering the author’s Amazon numbers, 40 years after his death, would be the envy of most living authors.

Merton’s affair with the nurse known as “M” also scandalizes those who think that monks never fall in love. (After both ended the relationship, a chastened Merton returned to his chastity.) Even the manner of his death raised suspicions. His last words to the Bangkok conference were, “So I will disappear from view and we can all have a Coke or something.” Friends dismiss rumors of suicide, attributing his death to a lifelong clumsiness.

But what raises the most suspicion is his longtime affinity for Eastern spiritual traditions. Merton’s trip to the Asian subcontinent and Southeast Asia, during which he described a mystical experience before a statue of the Buddha in Ceylon (now Sri Lanka), makes some traditional Catholics queasy, and gave rise to the now-widespread rumor that he planned to leave the monastery, or the church. This is false. In a letter a few weeks before his death in 1968, he wrote to a close friend, “Keep telling everyone that I am a monk of Gethsemani and intend to remain one all my days.”

The body of the bestselling author who corresponded with Boris Pasternak, Abraham Heschel and Pope John XXIII, was returned to his monastery with his worldly goods: rosary beads (broken), glasses, a small icon, a prayer book, a $10 Timex watch. A final paradox: the man who preached against war returned to the States in the belly of an Air Force bomber bringing back the bodies of dead soldiers from Vietnam. His grave in the abbey cemetery is next to the abbot who had denied him permission to travel, an irony that would have delighted this saint of paradoxes.