Mary Gordon — novelist, memoirist, professor of English at Barnard College — has long proved herself to be a Catholic voice engaged in deep and nuanced dialogue with the Church. She is fluent in its rhythms, its mysteries, its illuminations — and its darkness. She is a truth-teller, one not afraid to name her church’s sins, nor unwilling to see through its complexities to its radiant core.

Gordon’s capacity to dwell in duality, to circle her subject from all perspectives, to call it as she sees it, positions her squarely as a critic — both literary and cultural — robustly qualified to take on Thomas Merton, the celebrated mid-20th-century monk and writer with a worldwide ecumenical following. In her new slim but soulful volume, “On Thomas Merton,” Gordon plants herself on her firmest footing: “I wanted to write about him, writer to writer.”

She opens her exploration by pinpointing the tension at the heart of Merton: “(I)n becoming a Trappist,” she writes, “he entered an order devoted to silence, and yet his vocation was based on words.”

Merton, author most famously of “The Seven Storey Mountain,” belonged, Gordon writes, to the post-World War I period “when Catholicism was intellectually and aesthetically chic.” He was one of a heady crop of distinguished literary converts, along with G.K. Chesterton, Evelyn Waugh and Graham Greene.

Before he entered the monastery as a Trappist monk at Gethsemani, the abbey outside Louisville, Kentucky, Merton had been engaged in urgent conversation with the modern world. It’s a conversation that never ceased, not until the hour of his accidental electrocution in a Thai bathroom, some 20 miles outside Bangkok, in 1968. He’d been granted special permission to leave his hermitage to address a world interfaith conference, in a talk titled “Marxism and Monastic Perspectives.”

While Gordon begins her examination of Merton’s works on a sympathetic note, fully understanding “the conflict between being an artist in solitude and being a human in the world,” further adding that his is “a spiritual test that combines the ascetic and the aesthetic,” she cuts the writer-monk little critical slack. In her scope is a litany that includes Merton’s autobiography, “The Seven Storey Mountain,” his 1941 novel, “My Argument with the Gestapo,” and finally his seven-volume, 2,500-plus-page Journals — “longer than the whole of Proust,” Gordon notes.

It’s her bracing honesty along the way that makes her final coda so penetrating. Wrapping up her assessment of “My Argument with the Gestapo,” she writes, “more than likely he would have been marginalized or disappeared,” had he not gone on to publish “The Seven Storey Mountain.” No wonder the reader startles to attention when, one page later, Gordon declares the journals “Merton’s best writing.” She explains: “I detect a much greater sense of spiritual vitality in his journal passages than I do in his books that are self-consciously ‘spiritual.’ ”

Studded with excerpts, Gordon’s meticulous probing of literary Merton points the curious reader toward the richest veins — in effect mapping the Merton catalog, pointing out the places to begin, or, for a reader already well-versed, sharpening the prism through which he’s understood.

Because she’s regarded Merton with the necessary distance of critic, Gordon’s closing passages — in which she throws down her guard — rivets our attention.

She places him alongside those other martyrs of 1968, Martin Luther King Jr. and Robert Kennedy. The greatness of Merton, she writes, lies in his “life lived in all its imperfectability, reaching toward it in exaltation, pulling back in fear, in anguish, but insisting on the primacy of his praise as a man of God.”

It’s an intimate literary portrait, stitched through with Merton’s own threads. Ultimately, it’s a prayerful one. And the prayer echoes far beyond its final page.

Barbara Mahany’s latest book,“The Blessings of Motherprayer: Sacred Whispers of Mothering,” was published last spring.