What is "Kol Magid mi'Dan"?
Rashi: The voice of prophets who prophesize about you, that you will be exiled for serving the calf in Dan.
Radak: From Dan will come someone who will tell of the coming of the enemy 1 . It mentions Dan, for it is the border of Eretz Yisrael - "mi'Dan v'Ad Be'er Sheva. The same applies to Har Efrayim 2 .
Malbim: You heed the voice of the false Navi from Dan; Yaravam's calf (one of the two of them) was there, and it prophesizes Shalom for you.
Even though Dan was among the 10 tribes exiled over 80 years ago (refer to 3:6:4:2*), the Kusim (Nochrim that Sancheriv settled there in place of the Jews) considered themselves Jews (even if their conversion was dubious); it is reasonable that they would tell the Jews in Yehudah of Nebuchadnetzar's coming. (PF)
This implies that also Har Efrayim is the border of Eretz Yisrael. Surely it is not the northern or southern border. Shechem, in Efrayim, was in the middle of Eretz Yisrael from north to south (Makos 9b)! Perhaps it was on the eastern border (of Eretz Yisrael proper, excluding Ever ha'Yarden). Above (1:13), Radak said that Bavel is northeast of Eretz Yisrael. (PF)
What is "u'Mashmi'a Aven me'Har Efrayim"?
Targum Yonasan: [Prophets] give bad tidings about what will happen to you for serving the image that Michah set up in the mountain of Beis Efrayim. Rashi - even though [the 10 tribes] were exiled in the days of Sancheriv, the sin was still intact. Great is sin - it breaks before and after it. Before - from the days of Avraham, "va'Yirdof Ad Dan" (Bereishis 14:14) - when he reached Dan, he weakened, because his children were destined to serve idolatry there. After - at the time of the Churban, "Kol Magid mi'Dan."
Malbim: The other calf of Yaravam was in Beis Kel, which is in Har Efrayim (Shoftim 4:5). You believe their evil voice, and you do not want to repent.
What is "Aven"?
Rashi: It is breakage.
Radak: It is evil and sin, like "Amal va'Aven" (Tehilim 10:7). The verse repeats with similar words. Mashmi'a is like Magid.
