1)
Why will everyone bow and sing to Hashem?
1.
Radak: (He will put a Ru'ach on them.) "Ki Az Ehpoch El Amim Safah Berurah Likro Kulam b'Shem Hashem Le'avdo Shechem Echad" (Tzefanyah 3:9).
2.
Malbim: They will recognize that You conduct everything according to Your desire. They will no longer sing to other gods, only to You.
