To whom to they bow?
Radak: Once they bow to Hashem, and once they bow to their king - idolatry, which they made king over themselves. They join Hashem to another matter, to serve it. The Torah said "Lo Sa'asun Iti Elohei Chesef vEi'lohei Zahav Lo Sa'asu Lachem" (Shemos 20:20)!
Malbim: Those who bow to Tzva ha'Shamayim are Resha'im. Those who bow to Hashem, and swear to bow only to him, are Tzadikim.
What do we learn from "ha'Nishba'im Hashem veha'Nishba'im b'Malkam"?
Rashi: They swear in the name of Hashem, and return to swear in the name of their king - idolatry 1 . They make the idolatry primary - if you do not believe a Shevu'ah in the name of Hashem, I will swear to you in the name of idolatry!
Malbim: Refer to 1:5:1:2. Those who swear to their king, they are Beinonim. They do not serve Hashem, and not Ba'al. They do only what the king commands. If the king serves Hashem, they do like his deeds; if he serves Ba'al, they lean after him.
Radak: Targum Yonasan is like this.
