In the case of Judah, arraying oneself in foreign attire signified the desire to be like the Assyrians and others in every way, including the worship of pagan gods. Mackay helpfully explains that it is not as though the dress itself marked the people out as worshippers of pagan gods. Rather, the issue was their zeal to copy the fashions of the great empires of the day, Assyria or Egypt.... It was not just a matter of fashion, but of where their true desires lay. They modeled themselves on these foreigners because they wanted to be like them, and had lost sight of what God desired to see in his people.
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Israel actually had its own laws for dress (Numbers 15:38; Deuteronomy 22:12), which were not arbitrary but linked with religious loyalties (Numbers 15:39–40). So the issue at stake was indeed the distinctiveness (or lack thereof) of God's people. The leaders of fashion chose rather to be like the nations.
2 And so God determined to punish those who arrayed themselves in foreign attire.
8 And on the day of the LORD’s sacrifice “I will punish the officials and the king’s sons and all who array themselves in foreign attire.