(Exodus 17:12) records a detail that the Mekhilta found deeply instructive: "And the hands of Moses became heavy." Why did his hands grow heavy during the battle with Amalek? The rabbis drew a moral lesson about procrastination in the performance of commandments.
The Mekhilta explains: if Moses had not delayed in dispatching Joshua to fight — if he had not said (Exodus 17:9) "Choose men for us" instead of acting immediately himself — his hands would not have been wearied in this way. The heaviness was a consequence of his initial hesitation. By delegating the task rather than seizing the moment, Moses introduced a delay that came back to burden him physically.
The rabbis painted a vivid picture of just how heavy Moses' hands became. They said his hands grew as heavy as if two pitchers of water were hung upon them. This is not a casual metaphor — it conveys genuine physical suffering. The greatest prophet in Israel's history stood on a hilltop with arms that felt like they were weighed down with water jugs, struggling to maintain the posture that kept his people alive in battle.
The lesson extends far beyond Moses. The Mekhilta derives a general principle: one should never be lax in performing commandments. Every moment of delay carries consequences. What seems like a minor hesitation — saying "you go" instead of going yourself — can compound into a burden that is far heavier than the original task would have been.