Jeremiah 42:19 - Joseph Benson’s Commentary on the Old and New Testaments

The Lord hath said, Go ye not into Egypt The good prophet, knowing how much it concerned this people to believe and obey the message God had sent to them by him, repeats again what he had urged before, assuring them it was by the command of the Lord that he said it. Know certainly that I have admonished you this day Hebrew, בכם העידתי, have testified to you, or, admonished you before witnesses. “God commanded the Jews, by Moses, not to have any commerce with Egypt, that they might not practise the idolatrous customs of that country, (Leviticus 18:3,) with whose idolatries they had been defiled during their sojourning there. Afterward he often reproved them by his prophets for making alliances with Egypt. And there were particular reasons, at this time, for so severe a prohibition, as the words here and in the context import, namely, because the Jews either learned several of their idolatrous practices from the Egyptians, or, at least were confirmed in those evil customs by their example. Besides, it was the rival kingdom that contended for empire with the Babylonians; and so the Jews going into Egypt for protection was, in effect, refusing to submit themselves to the king of Babylon, to whom God had decreed the government of Judea and all the neighbouring countries, Jeremiah 27:6.” Lowth.