A passionate Zionist from the time of his first publications at the beginning of the century, Buber has always known how to infuse Zionism with a distinctive spirit. He has an unparalleled way of combining the preservation of the past with the struggle for the future. Now and always, he has reiterated that the renaissance of the Jewish people can only come about through a radical return to its great past and its living religious values. This has won him the hearts and minds of all the young people who, in their journey to a forgotten Judaism, were desperately looking for the spiritual content of that Judaism from which they had been estranged...
He, Buber, succeeded in awakening the souls these assimilated Jews. He succeeded because, with all his profound scholarship, he always remained a modern man in the best sense of the world. He was able to win over the youth because he didn't bury himself or Judaism under a great past, but knew how to rediscover the living roots of this past to build a greater future.--Hannah Arendt (1935) "A Guide for Youth: Martin Buber, in Hannah Arendt The Jewish Writings, 31-3.
l was alerted to the significance of Arendt's early writings by Judith Butler (recall). But Butler treats Arendt as a contrast to Buber largely because she treats Arendt, informed by a 1972 interview with Arendt, as a non-Zionist ("after 1943"). To be sure even in the 1930s Arendt can be quite critical of Buber: in "Antisemitism," Arendt treats "Buber's Zionism" as explaining Jewish "substance" by way of pseudophilosophical profundity. (The Jewish Writings, 56)*
As an aside, one may wonder why, in 1943, the midst of Nazi genocide, Arendt would have moved herself to the non-Zionist camp (at least in her memory thirty years later). The answer can be found in "Zionism Reconsidered" (originally published in 1944). There Arendt writes about her reaction to the (1942) Biltmore program and the (1944) Atlantic City Resolution in which Zionists claim the "whole of Palestine, undivided and undiminished' without mention of the fate of local Arabs.
Arendt's piece on Buber is important to Zionists because it reminds us of the constructive role that Buber's thought can play in the spiritual life of some would-be-Zionists (recall, by contrast, Hazony's dismissal of Buber). In her very brief 1935 essay (originally published in French), Arendt explictly couples Buber with two thinkers. First, with Luther: as fellow translators of the Bible into German. What they achieve is "to interpret the Bible poetically in another language, in accordance with its spirit." (See here for the French!) Second, she couples Buber with Mendelssohn (who also translated the Bible into German but into Hebrew letters in part so that Jews could learn German and emancipate into German life; it is clear that Arendt thinks that Mendelssohn's translation fails to conforms to the spirit of the original). She treats Mendelssohn as the "beginning" of German Jewish history and Buber as "the end." (It is worth reminding ourselves that in 1935, the situation for German Jews was certainly very bleak, but not yet catastrophic--so Arendt was prescient.)
Arendt treats the Bible as "the greatest Jewish possession." (33) It is the "indissoluble link that exists between all of Jewish history--even the most modern--and its great beginning." It is not entirely clear what Arendt means by "modern" in this piece. It is also not entirely clear when 'modernity' begins in Jewish history. I suspect it means the importation of 'philosophy' (in its Athenian guise) into mainstream (elite) Jewish thought. I believe this because the whole essay evokes Maimonides's Guide.+
So, according to Arendt, the significance of Buber is, first, is that he is a successful spiritual teacher of the young not despite his Zionism but because of it. Second, Buber's Zionism is a spiritual Zionism rooted in religious history (and not a rejection of religion). Third, this Zionism is Messianic in so far as it (treats the past) is oriented toward the future.** It is Messianic because Buber treats Zionism as a means for the Jews to make a "vital contribution to the history of mankind," (quoted by Arendt, 33; recall my distinction between negative and Messianic Zionism here and here). That is, for Arendt's Buber the meaning of Zionism has significance -- "the mission God gave" (32) -- to all of humanity. (Of course, it is not Messianic in the sense of embracing charismatic leaders; recall here.) In particular, Buber is praised for being "always aware of how his knowledge can be useful in practical terms; he never shuts out of the future in favor of the past." (32) That is, by reanimating the past, Buber (and there are traces of Spinoza here) embraces works.