John Gill Commentary Jeremiah 42:15

"now therefore hear ye the word of Jehovah, O remnant of Judah: Thus saith Jehovah of hosts, the God of Israel, If ye indeed set your faces to enter into Egypt, and go to sojourn there;" — Jeremiah 42:15 (ASV)

And now therefore hear the word of the Lord, you remnant of
Judah
A small remnant indeed, a few that were left in the land; who ought therefore to have admired the distinguishing goodness of Providence in preserving them in it; where they should have continued and made use of their privilege, to the glory of God and their mutual good: thus says the Lord of hosts, the God of Israel ;
the Lord of armies above and below, the Lord God omnipotent, and so able to protect them in their land; and who had a peculiar favour to Israel, and stood in a particular relation to them, and therefore would do it, of which they had no reason to doubt. But, disobliging him, what judgments might they not expect? if you wholly set your faces to enter into Egypt :
are resolved upon it, and are actually engaged in it; turning their faces from Judea towards Egypt, and obstinately pursuing it, nor can be reclaimed from it: the phrase expresses their resolution, impudence, and obstinacy: and go to sojourn there :
to be sojourners and strangers there, as their fathers had been before; the remembrance of which was enough to set them against going into Egypt any more.