Amalek

Rashi, in an interesting midrash, says that the reason Amalek attacked Bnei Yisrael shortly after they exited Egypt was for one odd--very odd-- reason. Rashi says that Bnei Yisrael was dealing dishonestly with weights and measurement (the passage immediately preceding this one) in the desert and that is why God had allowed Amalek to attack. The Netziv, being the realist that he is, asks the obvious question: "They had weights and measurement in the desert?" "Were there actually business dealings in the deserts?" How is it that sinning in this capacity historically provided the impetus for an attack by Amalek? 

The Netziv provides an understanding of weights and measurements that can be applied to the attack of Amalek. Cheating  by way of weights and measurements is the easiest way to steal because the customer does not know that he is being cheated. The only thing preventing someone from dealing dishonestly with weights and measurements is an awareness of God. Even though people won't notice, nothing escapes Divine Omniscience. Cheating in weights is not meant to be taken literally as the cause for Amalek. The sin is merely a symptom of a deeper, more inherent sin--lack of faith and awareness of God. The ultimate paradigm of this sin is the person who is more afraid of people seeing him as a thief but gives  no heed to the fact his actions are being noted by God himself. 

The Netziv goes further and addresses another puzzling Pasuk.

 "אֲשֶׁר קָרְךָ בַּדֶּרֶךְ וַיְזַנֵּב בְּךָ כָּל-הַנֶּחֱשָׁלִים אַחֲרֶיךָ וְאַתָּה עָיֵף וְיָגֵעַ וְלֹא יָרֵא אֱלֹהִים" (Deuteronomy 25:18).

The end of the Pasuk reads that someone was "not God fearing." However, the ambiguous phrase does not tell us who is not God fearing. Rashi reads it as Amalek not being God fearing while the Netziv reads it as Bnei Yisrael who are the ones not fearing God.  The real fault was lack of faith in God. For a people sustained so miraculously through Divine Providence to not believe in God is a true blow to God's name and, indeed, warrants an attack by a godless people such as Amalek. The Netziv explains that the one belief, above all, which a Jew must fight to preserve in this world is belief in God.