IN 1613, JAPAN was ruled, under the shogun, by about 200 feudal lords called daimyo, each with his own domain. One of the greatest of these daimyo was Date Masamune, the one-eyed Lord of Sendai. Though not a Christian himself, he was a protector of Christians at a moment when most of the lords were briskly helping the shogun to stamp Christianity out.

All during 1613, Lord Date was working on a quite extraordinary project. He had as refugees in his domain the crew of a wrecked Spanish ship. With their assistance, he had a galleon built, far larger than the usual Japanese junk. Then he sent it off on a combined trading mission and embassy to Mexico. As ambassadors he sent four of his low-ranking samurai and (to be their interpreter) an ambitious Franciscan monk named Luis Sotelo. The chief of mission was a middle-aged samurai named Hasekura Rokuemon, an obscure rural squire with an income of 60 koku a year. By contrast, Lord Date himself had an annual income of 625,000 koku.

The embassy accomplished little or nothing in Mexico -- the viceroy said he had no power to make a treaty with Japan -- and eventually it went on to Madrid and then to Rome, where Hasekura had an audience with Pope Paul V. He didn't get back to Japan until 1620.

All this is historic fact. There are many surviving documents, of which my favorite is a letter written by the Venetian ambassador to Rome in 1615, telling the doge what his very foreign colleague looked like. "He is a man of rather low size," Simon Contarini wrote, "stout and of a dark color, with an almost square face; . . . he is about 46 years of age; he has with him a retinue of 27 persons, looking uncommonly like their master."

To westerners, accustomed to seeing early Japan only through the eyes of other westerners, whether long-ago ones like Contarini or moderns like James Clavell (Shogun), an account by a Japanese novelist would be interesting just for the difference in point of view. Doubly interesting when the Japanese novelist is Shusaku Endo, one of the half-dozen leading Japanese writers now living.

But Endo has done far more than write a historical novel about an early and odd encounter between East and West. Taking the history of Hasekura's embassy as a mere base, he has written a really quite profound religious novel.

One of the oddities of that voyage was that all of the Japanese on it (except some of the sailors) converted to Christianity. None of them, however, did so sincerely. They were just infiltrating. The merchants on the galleon converted first, because they believed, correctly, they couldn't hope to trade in Mexico unless they did. Anything for profit was their motto, and they were quite open about it. (Endo makes some sly parallels with modern Japan here.)

The four samurai ambassadors converted much later, in Madrid, and they did it because they were persuaded they couldn't hope to accomplish Lord Date's mission otherwise.

As it turned out, they couldn't accomplish it anyway -- the whole seven-year trip was a failure -- and even if they had, it wouldn't have mattered. By the time they got back to Japan, the shogun had gathered nearly all power into his own hands, and Christianity was totally forbidden in all domains. Even for their seeming conversion, they wound up being severely punished. Sotelo, who returned to Japan separately, was caught and executed.

To this already ironic history, Endo adds another and supreme irony. He has Hasekura become genuinely a Christian after his return to Japan. But not the kind of Christian the bishops in Madrid thought they were baptizing -- that is, a promising colonial convert. Throughout the novel, Endo gradually distinguishes two kinds of Christianity. The first hint comes when the envoys meet a renegade Japanese monk living in a remote Indian village in Mexico. (The history of the mission contains no such details -- but it could have. The Japanese got around in the early 17th century.) They are astounded to find that the former monk is still a Christian. "I believe in my own Jesus," he tells them. "My Jesus is not to be found in the palatial cathedrals. He lives among these miserable Indians."

At the time Hasekura is totally unimpressed. If anything were to attract him to Christianity, it would be the palatial cathedrals. He is attracted to power and resplendence, not to the "ugly and filthy" figure he sees hanging on those omnipresent crucifixes in Mexico, Spain, and Italy.

If Father Sotelo (whom Endo renames Velasco and promotes to be a great-nephew of Balboa) had heard the renegade monk, he would have been unimpressed, too. He is a spiritual conquistador -- as, indeed, most Christian missionaries have been, and some still are. They serve the church militant.

But by the end of the book, Hasekura is a secret Christian, dying for the faith Lord Date doesn't even know he has. And Father Velasco, no longer dreaming of a bishopric, has also become an "ugly and filthy" Christian. Against all canon law, he has administered the last rites to one of the envoys who, when he realized the mission had failed, committed seppuku (better known in America as hara-kiri). He has collaborated in a small way with Buddhism. He has ceased to think he has special access to God's will. He has died a failure in nearly all eyes but his own. And at the end the two men are alike, and are heroes.

If all this makes the book sound gloomy, it isn't. It is calm and understated and brilliantly told. Simple on the surface, complex underneath. Something like a fable from an old tapestry. Endo does wonders at evoking the early 17th century, as it was both for Japanese and for Europeans. (One early realization for a western reader is how much larger a role smell played for the Japanese. There is even a special missionary smell detectable to their nostrils: "the smell of a man who has stifled his lust for women"). He uses, and effectively, the kind of repetition, almost a refrain, that we associate mainly with the chorus of a song, or perhaps with Homer and his wine-dark sea and rosy-fingered dawn. At first it seems odd in a novel, but it works. He alternates sections in the samurai's mind and sections in Father Velasco's (first-person for Velasco, third-person for Hasekura); and this duality of vision is what works best of all. Van C. Gessel's translation is fully worthy of all this.

If you're interested in how East and West really met, forget Kipling. Read Endo.