The U-turns performed by Rabbi Rafi Peretz – after promising that “my words are written in stone” last week and in the recent months – have once again proven that the involvement of rabbis in politics is bad for the rabbinate, bad for Judaism and bad for politics. Rabbis are not necessarily any better or worse than other politicians. But politicians who win a seat in the Knesset based only on the fact that they are rabbis – that is, they represent the world of idealized halachic/legal Judaism – are doomed to failure. Either they remain faithful to their rabbinical calling and thus fail in their political role, or they become politicians in every sense and are thus almost certain to betray their rabbinical mission and lose the faith of their followers.The involvement of rabbis in Israeli politics is a longstanding tradition. Via formal or informal “councils of great Torah leaders,” or via public rabbinical influence on politicians, they select “elected” representatives, form and disband political parties, approve coalition agreements, and on occasion, bring down governments. This heightened level of rabbinical involvement in Israeli politics is bad enough, but even worse is the role played by rabbis who themselves become active politiciansIn order to succeed, politicians must play by the rules of the political playing field. These require constant compromise, including on issues with real substance. Successful politicians know how to forge alliances but also how to break them when necessary; they know how to attack their opponents and sometimes even their colleagues; and they know how to present the situation in a way that serves their own interests, even if this means straying from the truth.Rabbis – who act as both spiritual leaders and halachic jurists (poskim) – are the very antithesis of politicians. To be worthy of their role as rabbinical and spiritual leaders, they must be beyond reproach. In their daily conduct, their speech, their treatment of others, and their commitment to halacha [Jewish law] and to integrity and ethical standards, they must serve as role models for their students and followers. These, and the general public as well, expect their rabbis to represent Judaism in the purest and most honest way, and to sanctify the name of God. Their commitment to these values must be absolute. Any failure to live up to them is not just a personal failure but can even denigrate everything they stand for in the eyes of the public.The same is true regarding substantive issues. Certainly, any religious politician is committed to abiding by halacha. But the commitment of rabbis to halachic rulings must be absolute with zero room for compromise on issues such as religion and state. For example, in the 1990s, a group of religious politicians asked Chief Rabbi Yitzhak Herzog to issue a halachic ruling on the character of Shabbat in the public space in Israel. In his response, Herzog wrote that the approach they were seeking to take was halachically forbidden, but that since they were politicians and not poskim, he was certain that they would use their common sense to arrive at the optimal outcome depending on the circumstances, even if this was not fully in accord with the precise demands of halacha. This response demonstrates the inherent difficulties facing rabbis who function as politicians. The tension between what is expected by halacha and the political reality is liable to stymie their ability to properly lead the public they seek to represent.Rabbis do not have to be marooned in study halls, cut off from reality. They, and the treasury of Jewish values they carry with them, have much to offer public life in Israel in the way of advice or information. But whenever they enter the cesspool of politics as active participants, they tarnish themselves, their image as rabbis and the Judaism they seek to represent. This is bad for the rabbis and bad for Judaism.The writer is the director of the Center for Religion, Nation and State at the Israel Democracy Institute, and lectures on law at the Peres Academic Center.