What is the meaning of "Tzofeh Efrayim Im Elokai"?
Rashi: They support for them their Nevi'im who draw them to the side of their idolatry.
Radak: Efrayim set up a lookout with its gods ? a false Navi, who says his Nevu'ah in the name of his god.
Malbim: You have great hatred for the seer of (sent to prophesize about) Efrayim, and my (Hoshe'a's) G-d. You were angry with the seer, for he prophesized punishment for you, and with my G-d, who sent him.
Why does it say "Navi Pach Yakosh Al Kol Derachav"?
Rashi: For true Nevi'im, they conceal pits to trap them. Malbim ? they did so amidst hatred of Hashem and His Nevi'im. They would trap them in order to kill them ? "Charu Shuchah Lelachdeni u'Fachim Tamnu l'Raglai" (Yirmeyah 18:22).
Radak: The [false] Navi is to Efrayim, in all its ways, like a trap that traps birds. So Efrayim was caught via the Nevi'im's words.
Why does it say "Mastemah b'Veis Elokav"?
Rashi: In the Beis ha'Mikdash they killed 1 Zecharyah 2 and wanted to kill Yirmeyah ? "Mishpat Maves la'Ish ha'Zeh" (Yirmeyah 26:11).
Radak #1: This is the house of the calves ? they are Efrayim's gods. The false Navi prophesizes there; he causes hatred between Efrayim and Hashem.
Radak citing Targum Yonasan: They increase stumbling in Beis ha'Mikdash of their G-d.