Czeslaw Milosz was on my mind nearly 20 years ago when I wrote a poem called The Master, a portrait of the exemplary poet, an ideal figure based on no one historical life but composed of impressions gleaned from many. In it I imagined the master's dwelling place as a solitary tower, like the one in Galway inhabited by W.B. Yeats in the 1920s, but when it came to imagining his advice to younger poets, I thought of Milosz. "Tell the truth," Milosz's shadow-self enjoins in the poem, "do not be afraid."

In print and in person, Milosz offers important lessons on how a poet ought to conduct himself. The standards he sets are hard and high, but they are the usual bases for the attainment of durable distinction in any life or art: honesty, courage and what T.S. Eliot once called "a condition of complete simplicity, costing not less than everything".

Milosz's honesty, for example, required him to resign from the diplomatic service of the People's Republic of Poland after the war and it eventually brought him to an exile's life in Berkeley, California, where he has lived for the past 40 years, working until retirement as a professor in the Slavic languages and literatures department of the university.

His courage was evident not only in this embrace of solitude, both personal and intellectual, but in the writing of The Captive Mind (1953), the prose book that made his name in the English-speaking world. This was at once an account of the temptations of Marxism, a rejection of them and a set of portraits of typical figures who had succumbed.

What made it more than a cold-war polemic was Milosz's inward feel for the attractions of the communist doctrine. There is a personal intensity, a sense that much is at stake, a feeling that "there but for the grace of God go I".

But it is the simplicity costing not less than everything that makes Milosz such an irresistible poet, capable of lyric rapture and tragic meditation, as ironic as he is candid:

"My Lord, I have loved strawberry jam

And the dark sweetness of a woman's body.

Also well-chilled vodka, herring in olive oil,

Scents, of cinnamon, of cloves,

So what kind of a prophet am I?"

Still, whether he liked it or not, Milosz couldn't avoid being caught up in the historical catastrophes of 20th-century Poland and feeling bound to speak of them (one of his later prose works is symptomatically entitled The Witness Of Poetry). And yet he never allowed any messianic or propagandist impulse to divert him from his artistic path.

Indeed, his whole writing life has involved a dialogue between the part of him in thrall to what he calls "rhythmical speech/Which grooms itself and of its own accord, moves on", and the part of him that asks: "What is poetry that cannot save nations and peoples?"

My awe of Milosz's achievement meant that I was shy of meeting him, but when we were introduced in Berkeley in the early 1980s by his translators Robert Hass and Robert Pinsky, I found myself immediately at my ease.

Hass and I were, like the master himself, Catholic by birth, so all of a sudden we were swopping stories about schooldays among the soutanes and the birettas, talking about the Church's preoccupation in those days with sins of impurity and about the abiding sense of the sacred that a Catholic upbringing instils. I left the meeting with a feeling of great privilege, a gratitude for the freedom and familiarity of our conversation, and a renewed awareness of the quickness of the man's poetic senses, the fortitude and scope of his intellectual life and the youthfulness of his creative powers.

Accidental resemblances between the life Milosz knew as a child in Lithuania and my own experiences growing up in rural Ulster have given an added intimacy to my reading of his poetry. Translation surely doesn't put a great gap between what is conjured up in Polish and in English by the words waggon, First Communion, blacksmith's shop, "apple trees, a river, the bend of a road" (from the preface to Treatise On Poetry).

When we read these words and others like them, we agree with the poet's slightly surprised yet deeply convinced statement of his vocation: "It seems I was called for this:/To glorify things just because they are."

These glorified things, however, shine in a light that is more than the simple light of nostalgic recall. Memory, obviously, is the source of the images, but the point of the poetry is not just to indulge in the pleasures of recollection.

The motive is an intense, even obstinate desire to keep people and places and names and actions - actions both valorous and atrocious - from being forgotten. Milosz is acutely aware of his covenant with the outnumbering dead and the experienced phenomena.

"To know and not to speak./In that way one forgets." So he declares in a poem about reading the Japanese poet Issa, and he continues: "What is pronounced strengthens itself,/What is not pronounced tends to non-existence."

When he writes such lines, Milosz raises his voice against every nihilism. He is a faith-wielder. What is uniquely convincing is the tone, a feeling that this voice is trustworthy, that it knows what it is talking about. It wins our confidence because its statements have about them the big-lettered clarity of the school-book primer and the steady-eyed reliability of the veteran. They are manifestly the work of one whose counsel to himself has been as follows:

"To find my home in one sentence, concise, as if hammered in metal. Not to enchant anybody ... An unnamed need for order, for rhythm, for form, which three words are opposed to chaos and nothingness."

Milosz is revered because he combines the archetypal roles of Orpheus and Tiresias, being capable of both rhapsody and rebuke. You would want him as your critic, your confessor, your boon companion, and every time you meet him, you realise that you did not overestimate him in any of these roles. And yet when you read him, his wisdom and abundance and acuity are made even more available to you.

His ongoingness is audible in every line. His work satisfies the appetite for seriousness and joy that the word "poetry" awakens in every language. He restores the child's eternity at the water's edge, but equally he registers the adult's dismay that his name is "writ on water", his mortal knowledge that "what was once great now appears small ... What could once smite, now smites no more".

He helps the rest of us to keep faith with those moments when we are suddenly alive to the sweetness of living in the body, yet he won't absolve us from the responsibilities and penalties of being part of the life of our times.