'Sing to the Lord' in the Bible

Sing to the Lord, for he has done magnificent things, let this be known throughout the earth!

Sing to the Lord a brand new song! Praise him from the horizon of the earth, you who go down to the sea, and everything that lives in it, you coastlands and those who live there!

Is this really the kind of fasting I want? Do I want a day when people merely humble themselves, bowing their heads like a reed and stretching out on sackcloth and ashes? Is this really what you call a fast, a day that is pleasing to the Lord?