John Calvin Reformed @genevareformer

Here now the Prophet expressly and avowedly exhorts the people to repent. By bidding Jerusalem to wash from wickedness her heart, that she might be saved, he shews that there was no remedy, except the Jews were reconciled to God; and that this could not be, except they repented of their sins.

Matthew Henry Presbyterian @wholebiblehenry

God's usual method is to warn before he wounds. In these verses, accordingly, God gives notice to the Jews of the general desolation that would shortly be brought upon them by a foreign invasion. This must be declared and published in all the cities of Judah and streets of Jerusalem, that all might hear and fear, and by this loud alarm be either brought to repentance or left inexcusable.

Commenting on Jeremiah 4:5-18

John Gill Reformed Baptist @doctorgill

O Jerusalem, wash thine heart from wickedness,.... These are the words of the prophet, or of God by the prophet, showing the cause of all their ruin and destruction, the wickedness of their hearts; and they are expressed in such form and language, as to be accommodated to the case of any unregenerate sinner: every man's heart is wicked, desperately wicked, even wickedness itself; everything...