Psalms 57:7

How strangely is the tune altered here! David's prayers and complaints, by the lively actings of faith, are here, all of a sudden, turned into praises and thanksgivings; his sackcloth is loosed, he is girded with gladness, and his hallelujahs are as fervent as his hosannas. This should make us in love with prayer, that, sooner or later, it will be swallowed up in praise. Observe, I. How he prepares himself for the duty of praise (Psa 57:7): My heart is fixed, O God! my heart is fixed. My heart is erect, or lifted up (so some), which was bowed down, Psa 57:6. My heart is fixed, 1. With reference to God's providences; it is prepared for every event, being stayed upon God, Psa 112:7; Isa 26:3. My heart is fixed, and then none of these things move me, Act 20:24. If by the grace of God we be brought into this even composed frame of spirit, we have great reason to be thankful. 2. With reference to the worship of God: My heart is fixed to sing and give praise. It is implied that the heart is the main thing required in all acts of devotion; nothing is done to purpose, in religion, further than it is done with the heart. The heart must be fixed, fixed for the duty, fitted and put in frame for it, fixed in the duty by a close application, attending on the Lord without distraction. II.

— Matthew Henry's Concise Commentary (public domain)

I will . . . praise--both with voice and instrument.

— Jamieson-Fausset-Brown Commentary (public domain)