Passover remains a beloved Jewish holiday, with the Seder one of the most popular Jewish rituals in Israel and North America. But the bitter hametz controversy about outlawing selling un-kosher-for-Passover products in Israel highlights a central contrast between the Israeli and American Jewish experiences. Most American Jewish identity is voluntary; much Israeli Judaism is compulsory. Most Israeli Jews approach Judaism as a rigorous system of rules and faith reinforced by God and the law. Although only 20 percent of Israelis define themselves as religious, one recent Ynet survey estimated that 71 percent of Israeli Jews believe in God. Keeping God central to Judaism, as Jews traditionally did, defines Judaism by its commandments. Even many Israelis who break the commandments still perceive Judaism as rooted in God's law. Moreover, living in a sovereign Jewish state, much Israeli Judaism becomes involuntary, either compulsory or automatic. The law forces Israeli Jews to marry and divorce via the rabbinate, but other Jewish elements are simply givens in Israel, from speaking Hebrew to observing Jewish holy days as national holidays. More fundamentally, the state's Jewishness shapes perceptions of Judaism as a force intimately linked to state power. BY CONTRAST, most North American Judaism is voluntary, divorced from the commandments, law, or even faith in God. With 13 percent of American Jews identifying as Orthodox, even adding the dwindling number of Conservative Jews who feel bound by Halacha, Jewish law, probably 80 percent of American Jews consider their Judaism optional. A 2006 Harris survey estimated that 79 percent of Americans believe in God, but 52 percent of American Jews doubt God's existence. In a country whose founders separated church and state, and belonging to a community that has fought public displays of religion, most American Jews are programmed not to view Judaism as compulsory. Obligatory Judaism is like a command economy, guaranteeing high levels of participation, communal unity, and conformity, but risking low levels of creativity and satisfaction. Voluntary Judaism is like a market economy, risking more chaos, deviation and alienation but frequently yielding greater originality and individual fulfillment. Judaism is fundamental to many Israelis: they cannot imagine their lives without God, and most Israelis would feel smothered if somehow prevented from, say, ever speaking Hebrew again. For many American Jews, Judaism is utilitarian, a pleasant addition to their lives but one of many identities, ideologies, and hobbies they juggle. This dizzying choice in a vast spiritual and ideological supermarket explains those alarmist surveys reporting growing numbers of American Jews saying they would not consider Israel's demise a personal tragedy. They are being honest. Americans live in a disposable culture - a recent Pew poll reported that more than 40 percent of American adults have changed faiths since childhood. With this contrast, to many Americans, Israeli Judaism, ensnared in a web of obligations, of mutually exclusive dos and don'ts, often appears harsh, rigid, narrow, joyless. Many committed American Jews are equally dumbfounded by the 24/7 Jews who follow every "minor" ritual, and by the supposedly secular (although clearly, deeply Jewish) Israelis, who flout the fundamental traditions. On the other hand, to many Israeli Jews, American Judaism is idiosyncratic, superficial, diluted, will o'the wisp, goofy. Many secular Israelis join their religious fellow citizens in viewing American Jewish phenomena such as mixed minyans, women rabbis, and warm, huggy, guitar-strumming, bongo-banging Friday night services, as not really Jewish. ISRAELI JEWS and American Jews should learn from each other. Just as David Ben-Gurion vowed during World War II to fight the Nazis as if there were no British White Paper, and the British as if there were no Nazis, Jews who feel obligated should embrace Judaism as if it were voluntary, and Jews who see Judaism as optional should embrace Judaism's "Thou shalts" and "shalt nots." Many religious Israelis should lighten up. Their prayer services and ritual observances should be less mechanical and infused with more joy and wonder. The Jewish studies in religious schools could be less rote and infused with more meaning. Even more important, the Israeli rabbinate must learn that trying to compel free agents in a liberal democracy to accept religion often repels them. For generations now, heavy-handed rabbis have alienated their fellow Israelis. At the same time, secular Israelis should stop blaming rabbis and learn from their American peers about rejecting all-or-nothing approaches, synthesizing tradition and modernity, and taking responsibility themselves for charting their own Jewish journeys. The values crisis so many people lament in Israel, the loss of community endemic to modern consumerist society, could be tempered by an active, thoughtful, rich engagement with Jewish ethics, rituals, traditions, learning and spirituality. Similarly, most American Jews should inject more humility, rigor, learning and commitment into their Judaism. Too many American Jews approach Judaism as a candy store, filled with sweets to sample, some regularly, others exceptionally; some are consumed quickly, others last longer. Too many American Jews are too casual about their rich inheritance and their special roles as links in this holy chain stretching back millennia. Too many American Jews reduce their Judaism to a pale imitation of modern American culture, incorporating the latest cultural trends rather than accepting Judaism as a meaningful system of alternative values that can insulate us from modern life's materialism, alienation, individuation and anomie. Traditionally, the Etz Chaim, the tree of life, served as a metaphor for Judaism, teaching that Judaism grows imperceptibly but steadily. Many Israeli Jews should remember that a tree must grow to live and thrive. Many American Jews must remember that without deep, nurturing, steadfast roots, a tree cannot stand - or survive. This Passover, both Israeli and American Jews should liberate themselves from their ruts, learning from each other to reap a lush Jewish harvest by Shavuot. The writer is professor of history at McGill University and the author of Why I Am a Zionist: Israel, Jewish Identity and the Challenges of Today. His next book Leading from the Center: Why Moderates Make the Best Presidents, will be published by Basic Books this spring.