John Calvin Commentary Psalms 57:7

"My heart is fixed, O God, my heart is fixed: I will sing, yea, I will sing praises." — Psalms 57:7 (ASV)

My heart is prepared, O God! Some read fixed, or confirmed, and the Hebrew word נכון, nacon, has that meaning as well as the other. If we adopt it, we must understand David as saying that he had carefully meditated on the praises he was about to offer; that he did not rush into a hurried and superficial performance of this service, as too many are apt to do, but approached it with steadfast purpose of heart.

I prefer, however, the other translation, which indicates that he was ready to begin the service with all cheerfulness and cordiality. And although, wherever this spirit is truly felt, it will lead to steadfastness in religious exercise, it is not without importance that the reader should be made aware of the significance of the word used here in the Hebrew.

The ready heart is here contrasted by David with the mere lip-service of the hypocrite, on the one hand, and with dead or sluggish service, on the other. He approached this voluntary sacrifice with a sincere fervor of spirit, casting aside sloth, and whatever might prove a hindrance in the duty.