What is the meaning of "k'Raf'i l'Yisrael v'Niglah Avon Efrayim"?
Rashi: When I will want to save them and heal them, their sins are revealed in front of Me. Malbim - the previous verse said that Yehudah's Chesed will yield a harvest when Hashem returns their captivity. Here it teaches that Yisrael will be different. Initially their sin was covered. When Hashem began to do good to them, and Yaravam ben Yo'ash returned the border of Yisrael from Levo Chamas until Yam ha'Aravah (Melachim II, 14:25), they began to sin openly. "Avon Efrayim" is crookedness in matters of Emunah Bein Adam la'Makom.
Radak (6:11): The cure was "he returned Damesek and Chamas to Yehudah" 1 (Melachim II, 14:28).
Radak citing Targum Yonasan: When will be demanded [punishment for] the liability of Yisrael, and the sins of Efrayim and evil of Shomron will be exposed (refer to 7:1:4:2).
Radak (14:28): Earlier, David captured them and they became of Yehudah.
What is "Ra'os Shomron"?
Malbim: It is their evil Bein Adam l'Chavero.
What Sheker did they do?
Malbim: This is Avon Efrayim - they lied about Emunas Hashem, and served idolatry.
What do we learn from "v'Ganov Yavo Pashat Gedud ba'Chutz"?
Rashi: They constantly covertly steal their colleagues' money, and even send their troops to openly rob people.
Radak citing Targum Yonasan: They did Sheker, and steal from houses at night, and rob in the Midbar during the day.
Malbim: This is Ra'os Shomron. Initially, only one stole, and covertly; now it is not one thief ? it is a whole troop, and they plunder openly.