For my heart was in a ferment. The Psalmist again returns to the confession which he had previously made, acknowledging that whilst he felt his heart pierced with perverse envy and emulation, he had complained against God, in a peevish or fretful manner. He compares his anger to leaven. Some translate, My heart was steeped in vinegar. But it is more suitable to explain the verb thus, My heart was soured or swollen, as dough is swollen by leaven. Thus Plautus, when speaking of a woman inflamed with anger, says that she is all in a ferment. [1] Some read the last clause of the verse, My reins were pierced; and they think that ', aleph, in the beginning of the word, 'stvnn, eshtonan, the verb for pierced, is put instead of h, he; [2] but this makes little difference as to the sense. We know that the word klyvt, kelayoth, by which the Hebrews denote the reins, comes from the verb kl', kalah, which signifies to desire, to covet earnestly, this word being put for the reins, because it is said that the desires of man have their seat in that part of the body. David therefore declares that these perplexing and troublesome thoughts had been, as it were, thorns which pierced him. [3] We have already stated how he came to be affected with this pungent and burning vexation of spirit. We will find many worldly men who, although they deny that the world is governed by the Providence of God, yet do not greatly disquiet themselves, but only laugh at the freaks of Fortune. On the other hand, true believers, the more firmly they are persuaded that God is the judge of the world, are the more afflicted when his procedure does not correspond to their wishes.

Footnotes

1 - Plautus' words are, "Mea uxor tota in fermento jacet;" "My wife lies all in a ferment." In like manner he says, "Ecquid habet acetum in pectore?" "Has he any vinegar in his breast?"

2 - This is Kimchi's and Houbigant's opinion.

3 - "The Hebrew verb [for pierced] indicates the acute pain felt from a sharp weapon. (See Parkhurst, on snn, iv.) Common experience shows that the workings of the mind, particularly the passions of joy, grief, and fear, have a very remarkable effect on the reins or kidneys." -- Mant

Thus my heart was grieved - literally, and more expressively, "was soured." The meaning is, that his heart was grieved, pained, dissatisfied. His mind was embittered, and he was rendered unhappy, by the views which he cherished about God, as doubting the wisdom and justice of his dealings with people - and about people, as being envious at their prosperity.
And I was pricked in my reins - The reins are often in the Scriptures represented as the seat of the thoughts or affections. See the notes at Psalm 7:9. The word rendered "pricked" means to sharpen, as a sword; and then, to pierce and penetrate as a sword does. The idea is, that these thoughts, so distressing and painful, seemed to be like a sharp sword penetrating to the seat of life.

Thus may heart was grieved - The different views which I got of this subject quite confounded me; I was equally astonished at their sudden overthrow and my own ignorance. I felt as if I were a beast in stupidity. I permitted my mind to be wholly occupied with sensible things, like the beasts that perish and did not look into a future state; nor did I consider, nor submit to, the wise designs of an unerring Providence.

Thus my heart was grieved,.... Not with his own sins, nor with the sins of the wicked, but at their prosperity; for this is an account of himself, while under the temptation, and before he went into the sanctuary of the Lord; or when he was "leavened" (r), with the old leaven of wickedness, and envy, and indignation; he was in a ferment, so Plautus (s) uses the phrase for being in anger and wrath; he swelled, as what is leavened does, against God and his providence: or was "soured" (t); he was out of humour and angry with God, or was exasperated and provoked at the favours bestowed upon the wicked. Some render it "inflamed" (u), made hot; not with the love of God, and meditation upon it, but with wrath and indignation:
and I was pricked in my reins; disturbed and distracted in his thoughts, felt a great deal of pain in his mind, while he was considering the prosperity of the wicked; which was as a sword in his bones, and as an arrow shot into his reins; see Lamentations 3:13.
(r) "effervesceret fermenti instar", Tigurine version; "in fermento esset", Cocceius; so Ainsworth. (s) Casina, Acts. 2. Sc. 5. v. 17. (t) Acescet Montanus; "quasi aceto acri perfundebatur", Vatablus. (u) "Inflammatum est", V. L.

God would not suffer his people to be tempted, if his grace were not sufficient, not only to save them from harm, but to make them gainers by it. This temptation, the working of envy and discontent, is very painful. In reflecting upon it, the psalmist owns it was his folly and ignorance thus to vex himself. If good men, at any time, through the surprise and strength of temptation, think, or speak, or act amiss, they will reflect upon it with sorrow and shame. We must ascribe our safety in temptation, and our victory, not to our own wisdom, but to the gracious presence of God with us, and Christ's intercession for us. All who commit themselves to God, shall be guided with the counsel both of his word and of his Spirit, the best counsellors here, and shall be received to his glory in another world; the believing hopes and prospects of which will reconcile us to all dark providences. And the psalmist was hereby quickened to cleave the closer to God. Heaven itself could not make us happy without the presence and love of our God. The world and all its glory vanishes. The body will fail by sickness, age, and death; when the flesh fails, the conduct, courage, and comfort fail. But Christ Jesus, our Lord, offers to be all in all to every poor sinner, who renounces all other portions and confidences. By sin we are all far from God. And a profession Christ, if we go on in sin, will increase our condemnation. May we draw near, and keep near, to our God, by faith and prayer, and find it good to do so. Those that with an upright heart put their trust in God, shall never want matter for thanksgiving to him. Blessed Lord, who hast so graciously promised to become our portion in the next world, prevent us from choosing any other in this.

He confesses how--
foolish--literally, "stupid," and
ignorant--literally, "not discerning," had been his course of thought.

Pricked - I was deeply wounded with disquieting thoughts.