They shall speak forth, etc. As the verb nv, nabang, means properly to gush out, some suppose, that, as applied to speech, it means not simply speaking, but an overflowing utterance, like water rushing from a fountain, and the verb yrnnv, yerannenu, in the close of the verse, answers to this, meaning to shout, or sing aloud. To celebrate the memory of the Lord's goodness, is the same with recalling to memory what we have personally experienced of his goodness. We cannot deny God's claim to praise in all his excellencies, but we are most sensibly affected by such proofs of his fatherly mercy as we have ourselves experienced. David makes use, therefore, of this alluring consideration to induce us the more readily and cheerfully to engage in the praises of God, or rather, (according to the figurative word already used,) to burst forth in celebration of them.

They shall abundantly utter the memory of thy great goodness - Hebrew, The memory of the greatness of thy goodness they will pour forth. The word rendered "abundantly utter" means to bud forth, to gush out, to flow, as a fountain. Proverbs 18:4; Proverbs 1:23; Proverbs 15:2, Proverbs 15:28. It is applied to words as poured forth in praise. The meaning is, that the heart is full, as a fountain is full of water, and that it naturally overflows, or seeks to discharge itself. The thought of the goodness of God fills the heart, and makes it overflow with gratitude.
And shall sing of thy righteousness - They shall shout for joy at the displays of thy justice; at the manifestations of thy righteous character.

They shall abundantly utter the memory of thy great goodness,.... Not only his essential goodness, or the perfections of his nature; nor his providential goodness only; but his special grace and goodness to his own people in becoming their surety, in assuming their nature, in laying down his life for them, in working out their salvation, in paying their debts, and providing for them food and raiment, and all things pertaining to life and godliness: which goodness is "great", inexpressibly great, and passing knowledge; if we consider the spring of it, his good will and free favour, and not the works and merits of men; the multitude of persons it reaches to, all the elect of God, a number which no man can number, out of every people and nation; and the many benefits bestowed on them through it, all the blessings of goodness he himself is prevented with, even all spiritual blessings that are in him. Now this will be remembered by the saints, and not forgotten; in "the memory" of which they are assisted by the Spirit of God, who brings this goodness to their remembrance; and under the Gospel dispensation an ordinance is appointed to refresh the memory of the saints with it; and with such helps they are enabled at times "abundantly" to "utter" it, or to speak of it in a very free and flowing manner; it comes from them like water from a flowing fountain, as the word (c) signifies; out of the abundance of their hearts, and the great sense they have of his goodness, their mouth speaketh;
and shall sing of thy righteousness; his essential righteousness as God, the same with his divine Father's; his righteousness as Mediator, or his righteous and faithful performance of his office, as such; and his justifying righteousness, which he undertook to work out and bring in: and those that know it, and have an interest in it, have great reason to sing, because it is commensurate to the demands of law and justice; and so large a robe of righteousness as to enwrap and cover all their persons, and justify them from all things; and because it is so beautiful, rich, and glorious, and makes them appear so; and because it is so well-pleasing to God, and so comfortable and beneficial to them; securing them from wrath, and entitling them to eternal life. Aben Ezra adds the word "saying", as if what follows was, the subject matter of the song.
(c) "eructabunt", Montanus, Piscator; "scaturient", Cocceius.

memory-- (Psalm 6:5), remembrance, or what causes to be remembered.
righteousness--as in Psalm 143:1, goodness according to covenant engagement.