1)
When will he sing a new Shirah to Elokim?
1.
Radak: Whenever You do new wonders with me.
2.
Malbim: It is for a supernatural miracle. Therefore, it will be on a harp of 10 strings, which hints to the world of intellectual [angels], and not on one of eight strings, which pertains to music of the Galgal (nature and the Ma'arachah).