When Moses’ hands – and the people’s faith – are flagging, Aaron and Hur, Moses’ brother and nephew, support him. But what is the underlying meaning of this story?
It seems that Scripture here is being intentionally obscure, only hinting at what it is actually trying to convey. In essence, the Torah is saying that something is missing in what Moses represents, that more people are needed to support Moses’ faith on either side of him. Thus, two other spiritual forces, a brother and a nephew, must support Jewish faith during the war with Amalek. From an historical perspective, it is clear that these forces were Christianity and Islam. Aaron symbolizes Christianity, and Hur – Islam.
Maimonides notes that God has given Islam and Christianity exceptional capacity for spreading the ideas of Judaism throughout the world. And that the affinity of those religions to Judaism also created conditions that were especially conducive to the survival of the Jews in exile, allowing them to live among their own “religious family,” as it were,
Indeed, we see that, in the long run, the Jews as a people survived in the diaspora only in Christian and Islamic countries. To be sure, the Jews’ relationship with those other two religions was a source of severe tension for many long centuries, and created enormous problems. But those relationships were ultimately what saved the Jewish people, and made it possible for them to earn and retain the extraordinary prominence that is now acknowledged and respected virtually everywhere in the world.
Life in the Jews’ own state likewise poses problems on a very large scale – a national scale. This is why Jewish faith in the Land of Israel is characterized by gadlut, “greatness.” When the Jews go into exile (that is, when Moses leaves the central battleground to ascend the hill), those problems assume a smaller scale, reduced to the level of the individual and the community. At that point Judaism has the status of katnut, “smallness” (Moses sitting on a stone). In such times, Christianity and Islam actually provide important support for the Jewish faith.
 Small communities of Jews existed in other countries – India, for example – but played no significant role in Jewish history. And in China, where the Jews experienced no conflict or issues with the surrounding population and culture, they completely assimilated and, practically speaking, almost entirely disappeared.