Why does the Torah repeat "al-Pi Hashem Yachanu, ve'al-Pi Hashem Yisa'u ... "?
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Seforno: To teach us that Yisrael followed instructions whether they encamped for an inconveniently short period or whether they traveled after they had encamped for a long time and were comfortably settled.
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2.
"Al-Pi Hashem Yachanu? teaches us that when they dismantled the Mishkan, it was as if they intended to re-erect it in the same location,
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and that consequently,someone who dismantles a building with the intention of re-erecting it elsewhere is Patur on Shabbos.
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