Midras Keluaran 17:11: Mekhilta DeRabbi Yishmael, Ein Yaakov (Glick Edition), Midrash Tanchuma Buber & Midrash Tanchuma

(Ibid. 11) "And it was, when Moses lifted his hand, that Israel prevailed, etc." Now do the hands of Moses strengthen Israel or break Amalek? Rather, whenever Moses lifted his hand heavenward, they gazed at it and affirmed their faith in Him who commanded Moses to do thus, and the Holy One Blessed be He wrought for them miracles and mighty acts.

(Fol. 29) MISHNAH: (Ex. 17, 11) And it came to pass when Moses held up his hand, Israel prevailed, etc. Do then the hands of Moses cause war to be waged or to cease? But the passage means to teach this lesson: VThen the Israelites looked upward and pledged their hearts to their Father in heaven, they prevailed; but when they ceased to do so, they failed. We find a similar instance also in (Num. 21, 8) Make unto thee a fiery serpent and set it on a pole, and every one that is bitten, when he looketh upon it shall live. Could, then, the serpent kill or bring to life? But the passage means to teach this lesson: When the Israelites looked upward for aid and pledged their hearts to their Father in heaven, they were healed; but when they did not, they perished.

(Exod. 17:11:) AND IT CAME TO PASS THAT, WHEN MOSES HELD UP <HIS HAND, ISRAEL PREVAILED>…. What happened in the end? (Vs. 13:) AND JOSHUA OVERTHREW (wayyahalosh, rt.: HLSh) <AMALEK AND HIS PEOPLE>…. R. Berekhyah the Priest said: He cast lots over them. <A lot> is called by four names: goral, pur, hevel, holesh (rt.: HLSh).¹⁴The verb wayyahalosh (rt.: HLSh) can have two meanings. The first is “overthrow” or some such word. The second is “cast lots.” Although the first meaning better fits the context of Exodus, R. Berekhyah adopts the second.