John Calvin Commentary Psalms 25:8

"Good and upright is Jehovah: Therefore will he instruct sinners in the way." — Psalms 25:8 (ASV)

Good and upright is Jehovah. Pausing for a little, as it were, in the course of his prayer, he occupies his thoughts with meditating on God's goodness, so that he may return to prayer with renewed fervor. The faithful feel that their hearts soon grow weak in prayer, unless they are constantly stirring themselves up to it with new encouragements; it is such a rare and difficult thing to persevere steadfastly and tirelessly in this duty.

Indeed, just as one must frequently add fuel to maintain a fire, so the practice of prayer requires the aid of such helps, so that it may not grow weak and eventually be entirely extinguished. David, therefore, desiring to encourage himself to persevere, speaks to himself and affirms that God is good and upright, so that, gathering new strength by meditating on this truth, he may return to prayer with greater eagerness.

But we must observe this consequence: since God is good and upright, he extends his hand to sinners to bring them back into the way. To attribute to God an uprightness that he might exercise only towards the worthy and the deserving is a cold view of his character and of little benefit to sinners, and yet the world commonly understands that God is good in no other way.

Why is it that scarcely one in a hundred applies God's mercy to himself, if not because people limit it to those who are worthy of it? No, on the contrary, it is said here that God gives proof of his uprightness when he shows transgressors the way; and this has the same meaning as calling them to repentance and teaching them to live uprightly.

Indeed, if God's goodness did not penetrate even to hell, no one would ever share in it. Let the Papists then boast as they please of their imaginary preparations, but let us regard this as a sure and certain doctrine: that if God does not prevent people with his grace, they will all utterly perish.

David, therefore, here commends this preventing grace, as it is called, which is shown either when God, in first calling us, renews our corrupt nature by the Spirit of regeneration, or when he brings us back into the right way after we have strayed from him by our sins. For since even those whom God receives as his disciples are here called sinners, it follows that he renews them by his Holy Spirit so that they may become teachable and obedient.