Albert Barnes Commentary Jeremiah 3:7

"And I said after she had done all these things, She will return unto me; but she returned not: and her treacherous sister Judah saw it." — Jeremiah 3:7 (ASV)

Or, “And I said (that is, within myself), After she has done all these things, she will return to me.” But she did not return.

Treacherous—literally, “Falsehood,” that is, false, faithless. The character of the two sisters is plainly marked. Samaria is apostate; she abandons Yahweh’s worship altogether. Judah maintains the form only; her secret desires are set upon the orgies of pagan worship.