Albert Barnes Commentary Jeremiah 3:10

"And yet for all this her treacherous sister Judah hath not returned unto me with her whole heart, but feignedly, saith Jehovah." — Jeremiah 3:10 (ASV)

Her treacherous sister Judah - These words are a sort of refrain, repeated three times (Jeremiah 3:7–8; Jeremiah 3:10), before God finally pronounces Judah more culpable than Israel.