John Gill Commentary Jeremiah 5:19

"And it shall come to pass, when ye shall say, Wherefore hath Jehovah our God done all these things unto us? then shalt thou say unto them, Like as ye have forsaken me, and served foreign gods in your land, so shall ye serve strangers in a land that is not yours." — Jeremiah 5:19 (ASV)

And it shall come to pass, when you shall say
That is, the people of the Jews, to whom the prophet belonged, after they had been spoiled by the enemy, and carried captive:

wherefore does the Lord our God all these things unto us ?
as if they were innocent and guiltless, and had done nothing to provoke the Lord to anger; and it may be observed, that they professed to know the Lord in words, and call him their God, though in works they had denied him; and they own the hand of the Lord in all those evils that would now be come upon them; though before they had said they were not spoken by the Lord, nor would they befall them, (Jeremiah 5:12) :

you shall then answer them ;
that is, the Prophet Jeremiah, in the name of the Lord:

like as you have forsaken me, and served strange gods in your land ;
when they were in their own land they forsook the worship and ordinances of God, and served the idols of the Gentiles, as the Targum rightly explains it:

so shall you serve strangers in a land that is not yours :
which some understand of strange gods; but rather it designs strange lords, as the Chaldeans in the land of Babylon, a land not theirs; and so it is measure for measure, a just retaliation in righteous judgment upon them.