He hath put a new song in my mouth; partly by giving me new matter or occasion for a song; and partly by inspiring me with the very words of it. Shall see it, i.e. shall observe God's wonderful mercies vouchsafed to me. And fear, i.e. shall stand in awe of that God, who by this instance they see to have so great power, either to save or to destroy, and tremble at his judgments, and give him that reverence, and worship, and obedience which he requires. Yet their fear shall not drive them from God, or bring them into despair, but shall draw them to God, and be attended with trusting in God.
Related Commentaries of Psalms 40:3
Psalms 40:3
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 the LORD.