Jehovah is merciful and gracious David seems to allude to the exclamation of Moses, recorded in Exodus 34:6, where the nature of God, revealed in a remarkable way, is more clearly described than in other places. When Moses was admitted to take a nearer view of the Divine glory than was usually obtained, he exclaimed upon beholding it, "O God! merciful and gracious, forgiving iniquity, slow to wrath, and abundant in goodness." As, therefore, he has summarily comprehended in that passage all that is important for us to know concerning the Divine character, David happily applies these terms, by which God is there described, to his present purpose. His design is to ascribe entirely to the goodness of God the fact that the Israelites, who by their own wickedness forfeited from time to time their relation to him, as his adopted people, nevertheless continued in that relation. Farther, we must understand in general, that the true knowledge of God corresponds to what faith discovers in the written Word; for it is not his will that we should search into his secret essence, except in so far as he makes himself known to us, a point worthy of our special notice. We see that whenever God is mentioned, the minds of men are perversely carried away to cold speculations, and fix their attention on things which can profit them nothing; while, in the meantime, they neglect those manifestations of his perfections which meet our eyes, and which afford a vivid reflection of his character. To whatever subjects men apply their minds, there is none from which they will derive greater advantage than from continual meditation on his wisdom, goodness, righteousness, and mercy; and especially the knowledge of his goodness is fitted both to build up our faith, and to illustrate his praises. Accordingly, Paul, in Ephesians 3:18, declares that our height, length, breadth, and depth, consists in knowing the unspeakable riches of grace, which have been manifested to us in Christ. This also is the reason why David, copying from Moses, magnifies by a variety of terms the mercy of God. In the first place, as we have no worse fault than that devilish arrogance which robs God of his due praise, and which yet is so deeply rooted in us, that it cannot be easily eradicated; God rises up, and that he may bring to nought the heaven-daring presumption of the flesh, asserts in lofty terms his own mercy, by which alone we stand. Again, when we ought to rely upon the grace of God, our minds tremble or waver, and there is nothing in which we find greater difficulty than to acknowledge that He is merciful to us. David, to meet and overcome this doubting state of mind, after the example of Moses, employs these synonymous terms: first, that God is merciful; secondly, that he is gracious; thirdly, that he patiently and compassionately bears with the sins of men; and, lastly, that he is abundant in mercy and goodness.

The Lord is merciful and gracious - See the notes at Psalm 78:38. The idea here is derived evidently from Exodus 34:6-7 - that great and glorious statement of God himself in regard to his own character. Our world is a different world under that statement from what it would be if that and kindred declarations had not been made. There is here a "progression" of thought; an "advance" on the previous statements. At first the psalmist referred to his own individual experience Psalm 103:3-5; then he referred to the dealings of God toward the Hebrew people Psalm 103:6-7; and now he rises to the general contemplation of his character as it relates to all mankind. It was a characteristic of God in respect to all, that he was kind, compassionate, and forbearing.
Slow to anger - That is, patient; not soon excited; bearing much, and bearing it long. See James 5:11; compare Exodus 34:6-7.
And plenteous in mercy - Margin, "great of mercy." The Hebrew word means "much," or great;" and the idea is, that mercy is not manifested by him in small or stinted measure. It is rich; full; abundant; overflowing; free.

The Lord is merciful - See the note on Psalm 86:15.

The Lord is merciful and gracious,.... So he made himself known to Moses, Exodus 34:6, and so David found him to be, and therefore calls upon his soul to bless his name. God is "merciful" in the most tender and affectionate manner; he has bowels of mercy, which yearn towards his people, as those of a tender parent to its child, as the word signifies; his mercy is free, without any motive or merit in men to engage it; he delights in showing it; he constantly bestows it; it is the source of all good things; it is communicated through Christ; all mercies temporal and spiritual come by him; and this lays a foundation for faith and hope: and he is gracious, as appears in the eternal choice of his people to salvation; in providing a Saviour and a ransom for them; in giving all grace and the blessings of it to them in his Son; in giving him for them, and all things to them with him; in justifying them by his righteousness; in pardoning their sins for his sake; in taking them into his family; in regenerating, calling, preserving, and saving them:
slow to anger, or "longsuffering" (d); even to wicked men, to the vessels of wrath, to the old world, yea, to Jezebel, to whom he gave space to repent; which longsuffering being abused and despised, is an aggravation of condemnation: but rather here it intends God's longsuffering to his people, as before conversion, waiting till the time comes that he is gracious to them; and after conversion, notwithstanding their backslidings and revoltings; and this longsuffering is their salvation:
and plenteous in mercy; large and abundant in it, as appears by the various instances of it, and ways and methods in which he shows it; in election, in the covenant, in redemption, in regeneration, in pardon and eternal life; and by the abundance of it which he bestows on every one of his people; and by the vast numbers which do partake of it.
(d) "longanimis", V. L. Junius & Tremellius, Piscator, Cocceius.

God's benevolence implies no merit. He shows it to sinners, who also are chastened for a time (Exodus 34:6).
keep (anger)--in Leviticus 19:18, bear a grudge (Jeremiah 3:5, Jeremiah 3:12).