Behold, thou hast instructed many - That is, thou hast instructed many how they ought to bear trials, and hast delivered important maxims to them on the great subject of the divine government. This is not designed to be irony, or to wound the feelings of Job. It is intended to recall to his mind the lessons which he had inculcated on others in times of calamity, and to show him how important it was now that he should reduce his own lessons to practice, and show their power in sustaining himself.
Thou hast strengthened the weak hands - That is, thou hast aided the feeble. The hands are the instruments by which we accomplish anything, and when they are weak, it is an indication of helplessness.

Thou hast instructed many - Thou hast seen many in affliction and distress, and thou hast given them such advice as was suitable to their state, and effectual to their relief; and by this means thou hast strengthened the weak hands, and the feeble knees - the desponding have been encouraged, and the irresolute confirmed and excited to prompt and proper actions, by thy counsel and example.

Behold, thou hast instructed many, and thou (b) hast strengthened the weak hands.
(b) You have comforted others in their afflictions but you cannot now comfort yourself.

Behold, thou hast instructed many,.... This is introduced with a "behold", either as a note of admiration, that such a man, who had instructed others, should act the part he now does; or as a note of attention to Job himself, and all others that should hear and read this, to observe it, and well consider it, and make the proper use of it; or as a note of asseveration, affirming it to be true and certain, notorious and unquestionable, as no doubt it was: Job was the instructor, a great man, and yet condescended to teach and instruct men in the best things, as did also Abraham, David, Solomon, and others; and a good man, and so fit to teach good things, as every good man is, and who, according to his ability, the gift and measure of grace received should instruct others; and a man of great gift he was, both in things natural, civil, and religious; one that could speak well, and to the purpose, and so was apt and able to teach; and such should not disuse and hide their talents: the persons he instructed were not only his own family, his children and servants, as Abraham before him did; but others who attended him, and waited for his counsel and advice, his words and doctrine, as for the rain, and latter rain, and which dropped and distilled as such, see Job 29:15; and these were "many"; his many ignorant neighbours about him, or many professors of religion, as there might be, and it seems there were in this idolatrous country; and many afflicted ones among these, which is usually the case: Job had many scholars in his school, of different sorts, that attended on him; and these he instructed in the knowledge of the true God, his nature, perfections, and works; and of the living Redeemer, his person, office, grace, and righteousness; and of themselves, the impurity of their nature through original sin, he was acquainted with; their impotency and inability to purge themselves, to atone for sin, and to justify and make themselves acceptable to God; as well as he instructed them in the worship of God, and the manner of it, their duty to him and to one another, and to all their fellow creatures: some render it, "thou hast corrected", or "reproved many" (l); he had taught the afflicted to be patient under their afflictions, and had reproved them for their impatience; and the design of Eliphaz is to upbraid him with it, as in Romans 2:21; thou that didst correct others for their unbecoming behaviour under afflictions, art thyself guilty of the same: "turpe est doctori, cure culpa redarguit ipsum":
and thou hast strengthened the weak hands; either such as hung down through want of food, by giving it to them, both corporeal and spiritual, which strengthens men's hearts, and so their hands; or through sluggishness, by exhorting and stirring them up to be active and diligent; or through fear of enemies, especially spiritual ones, as sin, Satan, and the world; by reason of whose numbers and strength good men are apt to be dispirited, and ready to castaway their spiritual armour, particularly the shield of faith and confidence in God, as faint hearted soldiers in war, to which the allusion is: and these were strengthened by telling them that all their enemies were conquered, and they were more than conquerors over them; that the victory was certain, and their warfare accomplished, or would quickly be: or else, whose hands were weak through a sense of sin and danger, and being in expectation of the wrath, and vengeance of God; and who were strengthened by observing to them that there was a Saviour appointed and expected, a living Redeemer, who would stand upon the earth in the latter day, and save them from their sins, and from wrath to come; see Isaiah 35:3; or rather, such whose hearts and hands were, weak through sore and heavy afflictions, whom Job strengthened by showing them that their afflictions were of God; not by chance, but by appointment, and according to the sovereign will of God; that they were for their good, either temporal, spiritual, or eternal; and that they would not continue always, but have an end; and therefore should be patiently bore, see 1-Corinthians 12:11.
(l) "corripuisti", Mercerus, Michaelis; "castigasti", Codurcus, Drusius, Schmidt, Schultens.

weak hands-- Isaiah 35:3; 2-Samuel 4:1.