Jamieson, Fausset and Brown on Jeremiah 3:5

5. he--"thou," the second person, had preceded. The change to the third person implies a putting away of God to a greater distance from them; instead of repenting and forsaking their idols, they merely deprecate the continuance of their punishment. Jr 3:12 and Psa 103:9, answer their question in the event of their penitence.

spoken and--rather (God's reply to them), "Thou hast spoken (thus), and yet (all the while) thou hast done evil," &c.

as thou couldest--with all thy might; with incorrigible persistency [Calvin].