If I sin - The object of this verse and the following is, evidently, to say that he was wholly perplexed. He did not know how to act. He could not understand the reason of the divine dealings, and he was wholly unable to explain them, and hence, he did not know how to act in a proper manner. It is expressive of a state of mind where the individual wishes to think and feel right, but where he finds so much to perplex him, that he does not know what to do. Job was sure that his friends were not right in the position which they maintained - that he was a sinner of enormous character, and that his sufferings were proof of this, and yet he did not know how to answer their arguments. He desired to have confidence in God, and yet he knew not how to reconcile his dealings with his sense of right. He felt that he was a friend of God, and he did not know why he should visit one who had this consciousness in this distressing and painful manner. His mind was perplexed, vacillating, embarrassed, and he did not know what to do or say. The truth in this whole argument was, that he was more often right than his friends, but that he, in common with them, had embraced some principles which he was compelled to admit to be true, or which he could not demonstrate to be false, which gave them greatly the advantage in the argument, and which they pressed upon him now with overwhelming force.
Then thou markest me - Dost carefully observe every fault. Why he did this, Job could not see. The same difficulty he expressed in Job 7:17-19; see the notes at that place.
And wilt not acquit me - Wilt not pardon me. Job did not understand why God would not do this. It was exceedingly perplexing to him that God held him to be guilty, and would not pardon him if he had sinned. The same perplexity he expressed in Job 7:21; see the note at that verse.

If I sin - From thee nothing can be hidden; if I sin, thou takest account of the transgression, and canst not hold me for innocent when thou knowest I am guilty.

If I sin, then thou markest me,.... Or "observest me" (t); that is, he took notice of his sins, strictly inquired into them and all the circumstances of them, watched the motions and progress of them, and carefully laid them up, in order to bring them out against him another day, and afflict or punish him for them; or he set a watch about him, "kept him in" (u), and enclosed him on every side with affliction, as if he was in a watch or prison, as Gersom; or, "wilt thou keep me" (w)? that is, in such close confinement: Gussetius (x) renders it, "if I have offered a sacrifice for sin", as the word is sometimes used; signifying, that though he should, as no doubt he did, offer sacrifice for himself, as it is certain he did for his children, yet even that was not regarded by the Lord; he still marked and observed him and his sins, and would not forgive him, or absolve him from his sins, as follows; see Job 7:12,
and thou wilt not acquit me from mine iniquity; clear him of it, and discharge him from it; pronounce him innocent, or pardon him; but, on the contrary, hold him guilty, and deal with him as such in a rigorous way; or wilt not "cleanse" or purify me, as the Targum and others (y), but let me continue, or treat me as an impure person, not fit for communion or converse.
(t) "observasti me", Beza, Mercerus; "tum observas me", Schmidt. (u) "Custodisti me", Drusius. (w) "Custodies me", Vatablus. (x) Ebr. Comment. p. 923. (y) "mundabis", Mercerus; "mundes", Pagninus, Montanus, Bolducius; "purges me", Junius & Tremellius.

Job did not deny that as a sinner he deserved his sufferings; but he thought that justice was executed upon him with peculiar rigour. His gloom, unbelief, and hard thoughts of God, were as much to be ascribed to Satan's inward temptations, and his anguish of soul, under the sense of God's displeasure, as to his outward trials, and remaining depravity. Our Creator, become in Christ our Redeemer also, will not destroy the work of his hands in any humble believer; but will renew him unto holiness, that he may enjoy eternal life. If anguish on earth renders the grave a desirable refuge, what will be their condition who are condemned to the blackness of darkness for ever? Let every sinner seek deliverance from that dreadful state, and every believer be thankful to Jesus, who delivereth from the wrath to come.

Job is perplexed because God "marks" every sin of his with such ceaseless rigor. Whether "wicked" (godless and a hypocrite) or "righteous" (comparatively sincere), God condemns and punishes alike.

Markest - If I am a wicked man, I cannot hide it from thee; and thou wilt punish me for it.