Why does it say "Sevavuni"?
Radak: I dwell amidst them. They surrounded Me, around the Beis ha'Mikdash, with their Avodah of other gods. Only Shevet Yehudah remained in the middle.
Malbim: Efrayim, the ruling Shevet, surrounded Me with denial. They denied foundations of Emunah, and said about the calves 'Eleh Elokecha Yisrael.'
To whom do "Efrayim" and "Beis Yisrael" refer?
Rashi: The kings of the 10 tribes and the entire nation, respectively.
Radak: It mentions Efrayim because Yaravam was from Efrayim. "Beis Yisrael" are the other tribes with Efrayim, except for Yehudah and Binyamin. The verse did not mention Binyamin, for Yehudah was primary, and the king was from Yehudah.
Malbim: Beis Yisrael are the other tribes. They engaged in Mirmah (deception Bein Adam l'Chavero), like it explains "Kena'an b'Yado Moznei Mirmah" (8).
What do we learn from "Od Rad Im Kel"?
Rashi: They still rule with fear of Elokim. "Rad" is like "v'Yerd mi'Yakov" (Bamidbar 24:19). Radak - and "Madu'a Amru Ami Radnu" (Yirmeyah 2:31). When Efrayim and the other Shevatim began to serve the calves, Yehudah still feared Hashem and served Him. Aviyah Melech Yehudah said to Yaravam and Yisrael "v'Atem Hamon Rav v'Imachem Eglei ha'Zahav; ... Kol ha'Ba Lemalei Yado b'Far Ben Bakar... v'Hayah Chohen l'Lo Elokim; va'Anachnu Hashem Elokeinu v'Lo Azavnuhu v'Chohanim Mesharsim la'Shem Bnei Aharon..." (Divrei ha'Yamim II, 13:8-10). "Rad Im Kel" is like "Ki Sarisa Im Elohim" (Bereishis 32:29).
Radak: It mentions authority, because when the king served Hashem, he rebuked the nation to serve only Hashem. When the king served other gods, he forced the nation to do similarly.
Radak citing Targum Yonasan: [Yehudah served Hashem] until Am Elokim 1 was exiled.
Malbim: In the days of Yosam and Chizkiyah they ruled with Yir'as Hashem in matters of Emunah.
Radak: He translates as if it says 'Am' with a Patach. This is astounding! Perhaps his tradition (of the text) was like this.
What do we learn from "v'Im Kedoshim Ne'eman"?
Radak: The matter is repeated in different words. "Kedoshim" is in place of Kel; the plural is used, like "Elokim Kedoshim Hu" (Yehoshua 24:19). Yehudah was Ne'eman (faithful) with Kel and persisted in His Avodah, even though Efrayim served the calves.
Radak citing his father: "Ne'eman" refers to Hashem.
Malbim: Ne'emanus is the opposite of Mirmah. He joins with Kedoshim to be faithful, and not deceive each other.