Who says "Beis Yakov Lechu
Rashi: The nations will say so to them. This refers to "v'Halchu Amim" (3).
Rashi citing Targum Yonasan: People of Beis Yakov will say so.
Radak, Malbim: These are the Navi's words to his generation. It says Beis Yakov, for above (3) it said that in the future, all the nations will say "go, and we will ascend." You (Yisrael), who are obligated and commanded from now 1 to go in the light of Hashem, "let us go in the light of Hashem!" It says "us", for the Navi includes himself, like I explained above (refer to 1:9:3:1**).
Chomas Anach citing Maharimat: (The Navi says so.) In the Midbar and while the Mikdashos stood, Yisrael were like Hashem's Arusah (Beis Yakov refers to women), on condition that we guard the Torah. We transgressed, and the Kidushin was Batel. In the future, we will stand in His Chatzer, which will be Nisu'in (entering the husband's Reshus), and we will cling to Hashem.
Radak explains so. Malbim says, the nations need to search amidst darkness to find Hashem in Tziyon. Hashem's light shines on you - all the more so you should ascend!
What is "Ohr Hashem"?
Radak: It is Torah and Mitzvos.
