Have mercy upon me, O God,.... David, under a sense of sin, does not run away from God, but applies unto him, and casts himself at his feet, and upon his mercy; which shows the view he had of his miserable condition, and that he saw there was mercy in God, which gave him hope; and upon his bended knees, and in the exercise of faith, he asks for it; according to thy lovingkindness; not according to his merits, nor according to the general mercy of God, which carnal men rely upon; but according to his everlasting and unchangeable love in Christ; from which as the source, and through whom as the medium, special mercy comes to the children of men. The acts of special mercy are according to the sovereign will of God: he is not moved to mercy neither by the merits nor misery of men, but by his free grace and favour; it is love that sets mercy to work: this is a most glaring gleam of Gospel light, which none of the inspired writers besides, except the Apostle Paul, saw, Eph 2:4; according unto the multitude of thy tender mercies blot out my transgressions; for his sin was complicated, attended with many others; and, besides, upon a view of this, he was led to observe all his other sins; and particularly the corruption of his nature, his original sin, which he mentions, Psa 51:5. These he desires might be "blotted out"; out of the book of account, out of God's debt book; that they might not stand against him, being debts he was not able to pay or make satisfaction for; and out of the table of his own heart and conscience, where they were ever before him, and seemed to be engraven; that they might be caused to pass from him, and he might have no more conscience of them; or that they might be blotted out, as a cloud by the clear shining of the sun of righteousness, with the healing of pardoning grace in his wings; or that they might be wiped away, as any faith is wiped from any person or thing: and all this "according to the multitude of his tender mercies". The mercy of God is plenteous and abundant; he is rich in it, and various are the instances of it; and it is exceeding tender, like that of a father to his children, or like that of a mother to the son of her womb; and from this abundant and tender mercy springs the forgiveness of sin, Luk 1:77. The psalmist makes mention of the multitude of the mercies of God, because of the multitude of his sins, which required a multitude of mercy to forgive, and to encourage his hope of it.