My wounds [1] have become putrid In this verse, he pleads the long continuance of his disease as an argument for obtaining some alleviation. When the Lord declares, concerning his Church, "that her warfare is accomplished, that her iniquity is pardoned, for she hath received of the Lord's hand double for all her sins," (Isaiah 40:2) his meaning is, that when he has sufficiently chastised his people, he is quickly pacified towards them; nay, more, that if he continue to manifest his displeasure for too long a time, he becomes through his mercy, as it were, weary of it, so that he hastens to give deliverance, as he says in another place, "For my name's sake will I defer mine anger, and for my praise will I refrain for thee, that I cut thee not off. Behold, I have refined thee, but not with silver; I have chosen thee in the furnace of affliction."-- (Isaiah 48:9, 10) The object, therefore, which David has in view, in complaining of the long continuance of his misery is, that when he had endured the punishment which he had merited, he might at length obtain deliverance. It was certainly no slight trial to this servant of God to be thus kept in continual languishing, and, as it were, to putrify and be dissolved into corruption in his miseries. In this his constancy is the more to be admired, for it neither broke down from the long period of delay, nor failed under the immense load of suffering. By using the term foolishness instead of sin, he does not seek in this way to extenuate his faults, as hypocrites do when they are unable to escape the charge of guilt; for in order to excuse themselves in part, they allege the false pretense of ignorance, pleading, and wishing it to be believed, that they erred through imprudence and inadvertence. But, according to a common mode of expression in the Hebrew language, by the use of the term foolishness, he acknowledges that he had been out of his right mind, when he obeyed the lusts of the flesh in opposition to God. The Spirit, by employing this term in so many places to designate crimes the most atrocious, does not certainly mean to extenuate the criminality of men, as if they were guilty merely of some slight offenses, but rather charges them with maniacal fury, because, blinded by unhallowed desires, they wilfully fly in the face of their Maker. Accordingly, sin is always conjoined with folly or, madness. It is in this sense that David speaks of his own foolishness; as if he had said, that he was void of reason and transported with madness, like the infatuated rage of wild beasts, when he neglected God and followed his own lusts.

Footnotes

1 - "The proper meaning of chkr is not a wound, but a bruise or wale made by a severe blow. My wales through my severe chastisement are become putrid and running sores." -- Fry

My wounds stink - The word rendered "wounds" here means properly the swelling or wales produced by stripes. See the notes at Isaiah 1:6; notes at Isaiah 53:5. The meaning here is, that he was under chastisement for his sin; that the stripes or blows on account of it had not only left a mark and produced a swelling, but that the skin itself had been broken, and that the flesh had become corrupt, and the sore offensive. Many expositors regard this as a mere figurative representation of the sorrow produced by the consciousness of sin; and of the loathsome nature of sin, but it seems to me that the whole connection rather requires us to understand it of bodily suffering, or of disease.
And are corrupt - The word used here - מקק mâqaq - means properly to melt; to pine away; and then, to flow, to run, as sores and ulcers do. The meaning here is, My sores run; to wit, with corrupt matter.
Because of my foolishness - Because of my sin, regarded as folly. Compare the notes at Psalm 14:1. The Scripture idea is that sin is the highest folly. Hence, the psalmist, at the same time that he confesses his sin, acknowledges also its foolishness. The idea of sin and that of folly become so blended together - or they are so entirely synonymous - that the one term may be used for the other.

My wounds stink and are corrupt - Taking this in connection with the rest of the Psalm, I do not see that we can understand the word in any figurative or metaphorical way. I believe they refer to some disease with which he was at this time afflicted; but whether the leprosy, the small pox, or some other disorder that had attacked the whole system, and showed its virulence on different parts of the outer surface, cannot be absolutely determined.
Because of my foolishness - This may either signify sin as the cause of his present affliction, or it may import an affliction which was the consequence of that foolish levity which prefers the momentary gratification of an irregular passion to health of body and peace of mind.

My wounds stink [and] are corrupt because of (f) my foolishness.
(f) That rather gave place to my own lusts, than to the will of God.

My wounds stink, and are corrupt,.... Meaning his sins, which had wounded him, and for which there is no healing but in a wounded Saviour, and by his stripes we are healed, Isaiah 53:5; where the same word is used as here; Christ's black and blue stripes and wounds, as the word signifies, are the healing of ours, both of sins, and of the effects of them; which, to a sensible sinner, are as nauseous and loathsome as an old wound that is festered and corrupt;
because of my foolishness: as all sin arises from foolishness, which is bound in the hearts of men, and from whence it arises, Mark 7:22; perhaps the psalmist may have respect to his folly with Bathsheba, which had been the occasion of all the distress that is spoken of both before and afterwards.

The loathsomeness, corruption, and wasting torture of severe physical disease set forth his mental anguish [Psalm 38:6]. It is possible some bodily disease was connected. The
loins are the seat of strength. His exhaustion left him only the power to groan [Psalm 38:9].

Foolishness - Sin.