How did they betray Hashem?
Radak: They intermarried with Nochrim and [served] their idolatry. This betrays Hashem who commanded "v'Lo Sischaten Bam ?Ki Yasir Es Bincha me'Acharai" (Devarim 6:3-4).
Radak citing Targum Yonasan: They were false to Hashem's word. They [father] children from daughters of the nations.
Why are their children called Zarim?
Rashi: [The parents] intermarried with Nochrim.
Radak: They went in the rites of the Nochrim. Targum Yonasan of "uv'Yaldei Nochrim Yaspiku" (Yeshayah 2:6) is uv'Nimusei Amemaya Azlin.
Malbim: This refers to Zecharyah ben Yaravam. His actions were Zar (foreign) to Hashem.
What Chodesh will consume them?
Rashi: Chodesh Av.
Radak #1: Chodesh Tamuz, in which the city wall was breached, and Chodesh Av, in which [the Mikdash] was destroyed.
Radak #2: This means in a short time, like a month ? "va'Achchid Es Sheloshes ha'Ro'im b'Yerach Echad" (Zecharyah 11:8).
Radak citing Targum Yonasan: The enemy will constantly consume them ? day by day, month by month.
Malbim: Shalum ben Yavesh, who will reign for one month in Shomron, will conspire against Zecharyah ben Yaravam, who reigned six months.
Why does it say "Es Chelkeihem"?
Radak: Soon will come the month in which the enemy will consume them and Chelkeihem, i.e. their fields and vineyards. This is like "v'Achlah Es ha'Chelek" (Amos 7:4), "Chelkas ha'Sadeh" (Bereishis 33:19).
Malbim: This finished off all of Beis Yehu.
