Charles Ellicott Commentary Psalms 40:3

"And he hath put a new song in my mouth, even praise unto our God: Many shall see it, and fear, And shall trust in Jehovah." — Psalms 40:3 (ASV)

New song. —See Psalms 33:3. It seems natural to suppose that this new song is incorporated here; that we have at least the substance of it, if not the words. Possibly the very words are taken up in Psalms 40:4. And we are to find the newness in the magnificent vindication of spiritual above formal worship.

Shall see it and fear. —Compare to Psalms 52:6, where there is plainly a reminiscence of this passage.