Charles H. Spurgeon on Psalms 40:3

And he hath put a new song in my mouth, even praise unto our God. At the passover, before his passion, our Lord sang one of the grand old Psalms of praise; but what is the music of his heart now, in the midst of his redeemed! What a song is that in which his glad heart for ever leads the chorus of the elect! Not Miriam's tabor nor Moses' triumphant hymn over Miriam's chivalry can for a moment rival that ever new and exulting song. Justice magnified and grace victorious; hell subdued and heaven glorified; death destroyed and immortality established; sin overthrown and righteousness resplendent; what a theme for a hymn in that day when our Lord drinketh the red wine new with us all in our heavenly Father's kingdom! Even on earth, and before his great passion, he foresaw the joy which was set before him, and was sustained by the prospect. Our God. The God of Jesus, the God of Israel, "my God and your God." How will we praise him, but ah! Jesus will be the chief player on our stringed instruments; he will lead the solemn hallelujah which shall go up from the sacramental host redeemed by blood. Many shall see it, and fear, and shall trust in the Lord. A multitude that no man can number shall see the griefs and triumphs of Jesus, shall tremble because of their sinful rejection of him, and then through grace shall receive faith and become trusters in Jehovah. Here is our Lord's reward. Here is the assurance which makes preachers bold and workers persevering. Reader, are you one among the many? Note the way of salvation, a sight, a fear, a trust! Do you know what these mean by possessing and practising them in your own soul? Trusting in the Lord is the evidence, nay, the essence of salvation. He who is a true believer is evidently redeemed from the dominion of sin and Satan.