My lips shall rejoice [1] when I sing to thee. In this verse David expresses more distinctly his resolution not to give thanks to God hypocritically, nor in a superficial manner, but to engage with unfeigned earnestness in this religious exercise. By the figures which he introduces, he briefly teaches us, that to praise God would be the source of his greatest pleasure; and thus he indirectly censures the profane mirth of those who, forgetting God, confine their congratulations to themselves in their prosperity. The scope of the last verse is to the same effect, implying that no joy would be sweet and desirable to him, but such as was connected with the praises of God, and that to celebrate his Redeemer's praises would afford him the greatest satisfaction and delight.

Footnotes

1 - "The original word rnn expresses a brisk, vibratory motion, like that of the lips in singing a lively air, or of the feet in dancing. Hence, figuratively, it signifies to rejoice or exult In this passage, it may be understood literally of the lips, and figuratively of the soul. And the English language having no corresponding verb which may be taken literally in reference to one subject, and figuratively in reference to another, it might be better to express its sense in connection with each, by two different verbs, thus: -- "My lips shall move briskly, when I sing unto thee, And my soul shall rejoice, which thou, etc." -- Horsley.

My lips shall greatly rejoice - My lips will seem to be happy in the privilege of celebrating the praises of God.
And my soul, which thou hast redeemed - Compare Psalm 34:22. The word soul here seems to be employed to denote "the soul" properly, as we understand the word - the immortal part. The usual meaning of the word, in the Psalm, however, is "life," and it is possible that the psalmist meant merely to say here that the "life" which had been spared should find pleasure in celebrating the praises of God; but there is no impropriety in supposing that he has reference to his higher - his immortal - nature.

My lips shall greatly rejoice and my soul - My lips shall use words expressive of my soul's happiness and gratitude. Thou hast redeemed me; and thou shalt have the eternal praise.

My lips shall greatly rejoice when I sing unto thee; and my (r) soul, which thou hast redeemed.
(r) For there is no true praising of God, unless it comes from the heart: and therefore he promises to delight in nothing, except that in which God is glorified.

My lips shall greatly rejoice when I sing unto thee,.... Both with vocal and instrumental music; this is praising the Lord with joyful lips, Psalm 63:5;
and my soul, which thou hast redeemed; signifying that it would not be lip labour, or bodily service, only that he should perform; but that his heart would go along with his lips in praise; and that under a sense of redeeming love, than which nothing can more strongly engage in such work, Psalm 103:1. For the redemption of the soul is exceeding precious; being the contrivance of infinite wisdom, the fruit of divine grace, and owing to the blood and sacrifice of Christ.