Infirmity - Bodily pain or trouble. "Spirit" in the Hebrew text is masculine in the first clause, feminine in the second, as though used in the latter as having lost its strength.

The spirit of a man will sustain - A man sustains the ills of his body, and the trials of life, by the strength and energy of his mind. But if the mind be scoundrel, if this be cast down, if slow-consuming care and grief have shot the dagger into the soul, what can then sustain the man? Nothing but the unseen God. Therefore, let the afflicted pray. A man's own spirit has, in general, sufficient fortitude to bear up under the unavoidable trials of life; but when the conscience is wounded by sin, and the soul is dying by iniquity, who can lift him up? God alone; for salvation is of the Lord.

The spirit of a man will sustain his infirmity; but (h) a wounded spirit who can bear?
(h) The mind can well bear the infirmity of the body, but when the spirit is wounded, it is hard to sustain.

The spirit of a man will sustain his infirmity,.... The spirit of a mighty man, as Jarchi; a man of spirit, that has a spirit of fortitude, even of natural fortitude, and especially of Christian fortitude; that has a spirit of might upon him, of power, and sound mind; a man of a Christian spirit, that is renewed in the spirit of his mind; who is a spiritual man, and has the Spirit of God in him, as well as a rational soul, an immaterial, immortal, and never dying substance. Such a man will bear up under many trials and exercises of life; will support under bodily infirmities; will take patiently the loss Of friends and of substance; endure reproach, and the loss of a good name, credit, and reputation, cheerfully, for righteousness's sake; and suffer persecution for the sake of Christ, and his Gospel, with an undaunted and unbroken spirit: the peace of conscience he feels within; the presence of God with him; the love of God shed abroad in his heart; seeing all his afflictions flowing from love, and working for his good; and having in view the glories of another world; he bears up under and goes through all afflictions with ease and pleasure; his conscience is clear, his heart is whole, his mind is easy; his wounds being healed, his sins pardoned, and his soul saved in Chris;
but a wounded spirit who can bear? or a "smitten" (w) one, smitten by the Lord; by the word of the Lord, which he uses as a hammer to break rocky hearts in pieces; by the law of God, which produces wrath, and a looking for of fiery indignation; by the Spirit of God, awakening the conscience, and convicting it of sin, righteousness, and judgment; which smitings are very grievous, though they tend to bring to repentance; are in order to healing, and are in love. Or, "a broken spirit" (x), as in Proverbs 17:22; broken with a sense of sin, and with an excess of sorrow for it; when a man becomes lifeless and hopeless, has no hope of life and salvation, and is in the utmost confusion; all his measures and purposes are broken, as well as his heart; he knows not what to do, nor what way to take; he is disconsolate, and refuses to be comforted; and which for the present is intolerable: though the Lord has a regard to such, is nigh unto them; has sent his son to bind up their broken hearts; yea, has himself been broken for them; and happy it is for them that they fall on him and are broken, and not he on them. Or, "a wounded spirit"; with a view of sin, as committed against the omniscient and omnipotent Being, a pure and holy God; a righteous one, whose nature is infinite; and so sin committed against him requires an infinite satisfaction, which a creature cannot give; and a God also, who is the author of their beings, and the Father of their mercies; all which makes sin against him the more cutting and wounding: likewise they are wounded with a view of the evil nature of sin, and the aggravated circumstances that attend it; and with the terrors of the law, that are set in array against them. And such a spirit "who can bear?" not without the sight of a wounded Saviour; or without a view of atonement by his sacrifice; or without the discoveries and applications of pardoning grace; or without a sense of peace and reconciliation made by the blood of Christ; or without some hope of salvation by him; and unless the good Samaritan pours in oil and wine into the wounds, and binds them up.
(w) "percussum", Pagninus, Baynus, Mercerus, Gejerus; "perculsum", Vatablus, Cocceius. (x) "Contritum", Montanus, Gejerus, Michaelis; "fractum", Junius & Tremellius, Piscator.

Firmness of mind supports under many pains and trials. But when the conscience is tortured with remorse, no human fortitude can bear the misery; what then will hell be?

infirmity--bodily sickness, or outward evil. The spirit, which sustains, being wounded, no support is left, except, as implied, in God.

14 The spirit of a man beareth his sickness;
But a broken spirit, who can bear it?
The breath of the Creator imparting life to man is spoken of as spiritus spirans, רוּח (רוּח חיּים), and as spiritus spiratus, נפשׁ (נפשׁ חיּה); the spirit (animus) is the primary, and the soul (anima) the secondary principle of life; the double gender of רוח is accounted for thus: when it is thought of as the primary, and thus in a certain degree (vid., Psychol. p. 103ff.) the manly principle, it is mas. (Genesis 6:3; Psalm 51:12, etc.). Here the change of gender is in the highest degree characteristic, and אישׁ also is intentionally used (cf. 1-Samuel 26:15) instead of אדם, 16a: the courageous spirit of a man which sustains or endures (כּלכּל R. כל, comprehendere, prehendere; Luther, "who knows how to contain himself in his sufferings;" cf. Psalm 51:12, "may the free Spirit hold me") the sickness [Siechthum] (we understand here "siech" in the old meaning = sick) with self-control, is generis masculini; while, on the contrary, the רוּח נכאה (as Proverbs 15:13; Proverbs 17:22), brought down from its manliness and superiority to disheartened passivity, is genere feminino (cf. Psalm 51:12 with Proverbs 18:19). Fleischer compares the Arab. proverb, thbât âlnfs bâlghdhâ thbât alrwh balghnâ, the soul has firmness by nourishment, the spirit by music.
(Note: In the Arab. language, influenced by philosophy, rwh, the anima vitalis, and nfs, the anima rationalis, are inverted; vid., Baudissin's Translationis antiquae Arab. libri Jobi quae supersunt (1870), p. 34.)
The question מי ישּׂאנּה is like Mark 9:50 : if the salt becomes tasteless, wherewith shall one season it? There is no seasoning for the spice that has become insipid. And for the spirit which is destined to bear the life and fortune of the person, if it is cast down by sufferings, there is no one to lift it up and sustain it. But is not God the Most High the lifter up and the bearer of the human spirit that has been crushed and broken? The answer is, that the manly spirit, 14a, is represented as strong in God; the discouraged, 14b, as not drawing from God the strength and support he ought to do. But passages such as Isaiah 66:2 do not bring it near that we think of the רוח נכאה as alienated from God. The spirit is נשׂא, the bearer of the personal and natural life with its functions, activities, and experiences. If the spirit is borne down to powerless and helpless passivity, then within the sphere of the human personality there is no other sustaining power that can supply its place.

Sustain - Will easily support him under any outward troubles. Wounded - Dejected with the sense of its own guilt and misery.