Musar על עבודה זרה 15:16

We must ask why the four empires , hosts of Israel in its various exiles, are mentioned in this Midrash at all? Our sages have described the Jewish people as serving idols in purity while in exile. Pardes Rimonim explains this by pointing out that G–d's bounty to Israel while they are in exile is directed via the respective שר, celestial representative of our host nation. G–d (16,16) is on record that: אני ה' השוכן אתם בתוך טומאתם, "I remain their G–d while dwelling amongst them in their impurity" (cf. Rashi on this verse). This is proof that sanctity still adheres to the Jewish people even in exile. The reasons for this, partially, is that G–d's praises emanate from the mouths of the Jewish people by reason of the food they consume. The Jewish people realise that it is G–d Who orders all food to grow in order that it may become the instrument of the people's sanctification.