For thou, O Lord! art good and propitious. We have here a confirmation of the whole preceding doctrine, derived from the nature of God. It would avail the afflicted nothing to have recourse to him, and to lift up their desires and prayers to heaven, were they not persuaded that he is a faithful rewarder of all who call upon him. The point upon which David now insists is, that God is bountiful and inclined to compassion, and that his mercy is so great, as to render it impossible for him to reject any who implore his aid. He calls God propitious, or ascribes to him the attribute of pardoning sin, which is a modification of his goodness. It were not enough for God to be good in general, did he not also extend to sinners his forgiving mercy, which is the meaning of the word slh, salach. Farther, although David magnifies the plenteousness of God's mercy, yet he immediately after represents this plenteousness as restricted to the faithful who call upon him, to teach us that those who, making no account of God, obstinately chafe upon the bit, deservedly perish in their calamities. At the same time, he uses the term all, that every man, without exception, from the greatest to the least, may be encouraged confidently to betake himself to the goodness and mercy of God.

For thou, Lord, art good - This is another reason why God should hear his prayer; and it is a reason which may be properly urged at all times, and by all classes of persons. It is founded on the benevolence of God; on the fullness of his mercy to all that invoke his name. We should call in vain on a God who was not merciful and ready to forgive; but in the divine character there is the most ample foundation for such an appeal. In his benevolence; in his readiness to forgive; in the plenitude of his mercy, God is all that a penitent sinner could wish him to be. For if such a sinner should endeavor to describe what he would desire to find in God as a ground of appeal in his prayers, he could not express his feelings in language more full and free than God has himself employed about his own readiness to pardon and save. The language of the Bible on this subject would express, better than any language which he could himself employ, what in those circumstances he would wish to find God to be.

For thou, Lord, art good - I found my expectations of help on thy own goodness through which thou art always ready to forgive. And I found it also on thy well-known character, to which all thy followers bear testimony, viz., that "thou art plenteous in mercy unto all them that call upon thee."

For thou, Lord, [art] good, and (d) ready to forgive; and plenteous in mercy unto all them that call upon thee.
(d) He confesses that God is good to all but only merciful to poor sinners.

For thou, Lord, art good,.... Essentially and independently good, from whom every good and perfect gift comes; good in himself, and good to others; good to all, in a providential way; and good to his own special people in a way of grace: this is asserted by Christ, Matthew 19:17.
and ready to forgive; there is forgiveness with him, and it is to be had without difficulty; he has largely provided for it; he is forward unto it, he freely giving it; it is according to the riches of his grace; he does abundantly pardon; no sooner is it asked but it is had; this David knew by experience, Psalm 32:5,
and plenteous in mercy unto all them that call upon thee; in truth, in sincerity, in a right way, through Christ, and faith in him; to such not only the Lord shows himself merciful, but is rich and abundant in mercy; he has a multitude of tender mercies, and abounds in his grace and goodness, and in the donation of it to his people; all which encourage their faith and hope in their petitions to him.

unto all . . . that call upon thee--or, "worship Thee" (Psalm 50:15; Psalm 91:15) however undeserving (Exodus 34:6; Leviticus 11:9-13).