Exodus 17:12

12When
Literally “now the hands of Moses,” the disjunctive vav (ו) introduces a circumstantial clause here – of time.
the hands of Moses became heavy,
The term used here is the adjective כְּבֵדִים (kevedim). It means “heavy,” but in this context the idea is more that of being tired. This is the important word that was used in the plague stories: when the heart of Pharaoh was hard, then the Israelites did not gain their freedom or victory. Likewise here, when the staff was lowered because Moses’ hands were “heavy,” Israel started to lose.
they took a stone and put it under him, and Aaron and Hur held up his hands, one on one side and one on the other,
Heb “from this, one, and from this, one.”
and so his hands were steady
The word “steady” is אֱמוּנָה (’emuna) from the root אָמַן (’aman). The word usually means “faithfulness.” Here is a good illustration of the basic idea of the word – firm, steady, reliable, dependable. There may be a double entendre here; on the one hand it simply says that his hands were stayed so that Israel might win, but on the other hand it is portraying Moses as steady, firm, reliable, faithful. The point is that whatever God commissioned as the means or agency of power – to Moses a staff, to the Christians the Spirit – the people of God had to know that the victory came from God alone.
until the sun went down.
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