Since biblical times, Jews have indulged in outlandish dreams: of redemption, of ingathered exiles, of peace on earth.

With the emergence of modern Zionism a century ago, Jewish leaders turned some of these dreams into reality. The return of the Jews to their land; the revival of the Hebrew language; the creation of an organic Israeli culture; the establishment of industry, commerce, and fiery military ability — all these happened because Jews were willing to make dreams real through concerted action, absolute conviction, and the channeling of skills and resources from all over the world. In Israel they created a legal system, an army, a parliament, an economy, a civilization that borrows from everywhere but is wholly its own.

The biggest danger with dreams is, of course, that sometimes they are not just bold but impossible. Many Zionist projects were realized precisely because they were built not on ignorance of the past but on its meticulous consideration. David Ben-Gurion, Israel’s first prime minister, who did more than anyone else to make Israel a reality, was schooled in the history of nations, and always tempered his boldness with an acute awareness of the limits of human endeavor.

Not so with Shimon Peres. A man blessed with luminous talents in organization, management, language, communication, and diplomacy, he became one of Ben-Gurion’s most important confidants by the age 35. Mr. Peres’s most striking trait has always been his inability to distinguish vision from frightful illusion.

Michael Bar-Zohar’s “Shimon Peres” (Random House, 480 pages, $29.95) teaches us a great deal about both the greatness and folly of Mr. Peres. We learn how, in the early 1950s, when the new state was most vulnerable to Arab attack, the young Mr. Peres led a wild, epic, and shockingly successful campaign to procure arms, despite massive Western embargoes, through intrigue, fund raising, underworld dealing, grand statesmanship, masterful bargaining, and dramatic persuasion. (Fighter planes, for example, were purchased in parts, assembled on a remote airfield in Burbank, Calif., and then secretly flown by Jewish volunteer aviators, over the North Pole, to Israel.) In the 1960s, Mr. Peres was the most active proponent of Israel’s nuclear efforts, and the tale of how he fought off internal opposition and international truculence to persuade France, a state barely nuclear itself, to furnish Israel with the technology to launch itself to world-power status, just hours before the French government fell, is nothing short of breathtaking.

And then there are the follies — misguided visions that were only stopped short thanks to the judgment of his superiors, especially Ben-Gurion. One thinks of his 1957 scheme to lease French Guyana from France and create an Israeli colony there — at a time when nine-year-old Israel was desperate for immigrants and struggling to establish itself. Or of the draft agreement he hammered out with West Germany in 1961, to allow the creation of German military bases on Israeli soil less than two decades after the Holocaust — a move that, had it even been floated, could have destroyed both his and Ben-Gurion’s political careers.

Yet of all his dreams, none has been bolder, more controversial, or more dismissive of history than the 1993 Oslo accords. Under Mr. Peres’s persuasion, the Israeli government invited Yasser Arafat, the founder of modern terrorism, to create a Palestine Liberation Organization city-state within rocket-propelled-grenade range of Israel’s population centers. With the support of Western arms and billions of dollars, Arafat took the deal, being careful never to promise an end to his struggle against Israel. “People tend to remember more and think less,” Mr. Peres wrote in “The New Middle East,” his 1993 manifesto defending the accords. “Our thoughts, which concentrate on the unfamiliar, are less welcome. However, we must focus on this new Middle East reality … and not wander among memories of victories in long-gone wars — wars that will never be fought again.” Critics of Oslo pointed to Arafat’s unambiguous record of hostility to Israel, double-dealing, and ruthlessness. For Mr. Peres, however, history was not a source of wisdom, but a burden.

The results are well known. Fourteen years later, the Palestinian Arabs have plunged into an abyss of corruption, terrorism, fundamentalism, anarchy, and fear. Israelis have become less secure, and world terrorism has raged, in part because of the encouragement that Oslo and subsequent capitulations have given it. Before Oslo, Western countries, led by Israel and America, systematically refused to negotiate with terrorists. Oslo shifted the winds, terror began to pay off, and things have not been the same since.

Like old Marxists who still defend the Soviet experiment in theory but dismiss its failures as bad implementation, Mr. Peres clings to the righteousness of Oslo but decries Arafat’s execution. “Without Arafat,” he said, “the Oslo accords wouldn’t have been signed. With Arafat, they couldn’t be implemented.” But impossible dreams, one is forced to conclude, really should not be pursued.

Mr. Bar-Zohar is not a masterful storyteller. His book is filled with linguistic infelicities, gullible readings of politicians’ manipulations, and a bleak uninterest in serious analysis of the historical events he describes. While highlighting many of Mr. Peres’s “mistakes,” he makes almost no effort to explain why Mr. Peres continues to make them. Mr. Bar-Zohar’s only attempt comes at the very end of the book. “The truth about Peres is simple: He cannot stop,” he writes. “Like a swimmer, who would sink and drown if he didn’t keep moving … Peres cannot stop either. His eyes, as always, look far into the future.” This conclusion, that Mr. Peres disdains the past and is indefatigable about the future, is not very satisfying after nearly 500 pages. Instead of offering insight, Mr. Bar-Zohar seems captivated by the projected selfimage of his subject.

But despite its major flaws, “Shimon Peres” shows us the world of a dreamer. We learn both the importance of vivid dreams and their enduring peril. Israelis, long schooled in the power of dreams, are now recovering from the trauma of Oslo’s failure — a trauma that has driven many young Israelis to abandon dreams altogether, to seek out a life of normalcy, to give up on Zionism or to leave the country.

This situation, indeed, is the greatest challenge facing both Israel and the West today. From American designs overseas to Europe’s dream of unity, Westerners are constantly promoting and debunking dreams as they seek a better world. We need nothing if not guidance as to how to keep on believing in bold dreams, to avoid impossible ones, and to be wise enough to tell them apart. Mr. Peres’s story, if nothing else, is a cautionary tale.

Mr. Hazony is the editor in chief of Azure, a journal of public affairs published by the Shalem Center. He lives in Jerusalem.