The following is an excerpt taken from page 38 of Heart Aflame: Daily Readings from Calvin in the Psalms.
FEBRUARY 7 Day 38
Keep me safe, O God, for in you I take refuge. This is a prayer in which David commits himself to the protection of God. God is ready to succour all of us, provided we rely upon him with a sure and stedfast faith; and that he takes under his protection none but those who commit themselves to him with their whole heart.
You are my Lord, my well-doing cannot extend to you.* David begins by stating that he can bestow nothing upon God, not only because God stands in no need of anything, but also because mortal man cannot merit the favour of God by any service which he can perform to him. At the same time, however, he takes courage, and, as God accepts our devotion, and the service which we yield to him, David protests that he will be one of his servants.
Two things are distinctly laid down in this verse. The first is, that God has a right to require of us whatever he pleases, seeing we are fully bound to him as our rightful proprietor and Lord. David, by ascribing to him the power and the dominion of Lord, declares that both himself and all he possessed are the property of God.
Let men strive ever so much to lay themselves out for God, yet they can bring no advantage to him. Our goodness extends not to him, not only because, having in himself alone an all-sufficiency, he stands in need of nothing, but also because we are empty and destitute of all good things, and have nothing with which to show ourselves liberal towards him.
It is impossible for men, by any merits of their own, to bring God under obligation to them, so as to make him their debtor. The sum of the discourse is, that when we come before God, we must lay aside all presumption. When we imagine that there is any good thing in us, we need not wonder if he reject us, as we thus take away from him a principal part of the honour which is his due. On the contrary, if we acknowledge that all the services which we can yield to him are in themselves things of nought, and undeserving of any recompense, this humility is as a perfume of a sweet odour, which will procure for them acceptance with God.
Excerpt taken from page 38 of Heart Aflame: Daily Readings from Calvin in the Psalms by John Calvin, copyright 1999, P&R Publishing.