They shall go down - That is, my hopes shall go down. All the expectations that I have cherished of life and happiness, will descend there with me. We have a similar expression when we say, that a man "has buried his hopes in the grave," when he loses an only son.
To the bars of the pit - "Bars of Sheol" - שׁאול בד bad she'ôl. Vulgate, "Profoundest deep." Septuagint, εἰς ᾅδην eis hadēn - to Hades. Sheol, or Hades, was supposed to be under the earth. Its entrance was by the grave as a gate that led to it. It was protected by bars - as prisons are - so that those who entered there could not escape; see the notes at Isaiah 14:9. It was a dark, gloomy dwelling, far away from light, and from the comforts which people enjoy in this life; see Job 10:21-22. To that dark world Job expected soon to descend; and though he did not regard that as properly a place of punishment, yet it was not a place of positive joy. It was a gloomy and wretched world - the land of darkness and of the shadow of death; and he looked to the certainty of going there not with joy, but with anguish and distress of heart. Had Job been favored with the clear and elevated views of heaven which we have in the Christian revelation, death to him would have lost its gloom.
We wonder, often, that so good a man expressed such a dread of death, and that he did not look more calmly into the future world. But to do him justice, we should place ourselves in his situation. We should lay aside all that is cheerful and glad in the views of heaven which Christianity has given us. We should look upon the future world as the shadow of death; a land of gloom and spectres; a place beneath the ground - dark, chilly, repulsive; and we shall cease to wonder at the expressions of even so good a man at the prospect of death. When we look at him, we should remember with thankfulness the different views which we have of the future world, and the source to which we owe them. To us, if we are pious in any measure as Job was, death is the avenue, not to a world of gloom, but to a world of light and glory. It opens into heaven. There is no gloom, no darkness, no sorrow. There all are happy; and there all that is mysterious in this life is made plain - all that is sad is succeeded by eternal joy. These views we owe to that gospel which has brought life and immortality to light; and when we think of death and the future world, when from the midst of woes and sorrows we are compelled to look out on eternity, let us rejoice that we are not constrained to look forward with the sad forebodings of the Sage of Uz, but that we may think of the grave cheered by the strong consolations of Christian hope of the glorious resurrection.
When our rest together is in the dust - The rest of me and my hopes. My hopes and myself will expire together.

They shall go down to the bars of the pit - All that I have must descend into the depths of the grave. Thither are we all going; and there alone can I rest. בדי baddey, which we translate bars, signifies also branches, distended limbs, or claws, and may here refer either to a personification of the grave, a monster who seizes on human bodies, and keeps them fast in his deadly gripe; or to the different branching-off-alleys in subterranean cemeteries, or catacombs, in which niches are made for the reception of different bodies.
When our rest together is in the dust - That is, according to some critics, My hope and myself shall descend together into the grave. It shall never be realized, for the time of my departure is at hand.
In those times what deep shades hung on the state of man after death, and on every thing pertaining to the eternal world! Perplexity and uncertainty were the consequences; and a corresponding gloom often dwelt on the minds of even the best of the Old Testament believers. Job's friends, though learned in all the wisdom of the Arabians, connected with the advantages derivable from the Mosaic writings, and perhaps those of the earlier prophets, had little clear or distinct in their minds relative to all subjects post mortem, or of the invisible world. Job himself, though sometimes strongly confident, is often harassed with doubts and fears upon the subject, insomuch that his sayings and experience often appear contradictory. Perhaps it could not be otherwise; the true light was not then come: Jesus alone brought life and immortality to light by his Gospel.

(p) They shall go down to the bars of the pit, when [our] rest together [is] in the dust.
(p) All worldly hope and prosperity fail which you say, are only signs of God's favour but seeing that these things perish, I set my hope in God and in the life everlasting.

They shall go down to the bars of the pit,.... He himself, and his friends, and the hopes they would have him entertain; these should all go down together to the grave, and there lie barred and locked up; these hopes, so as never to rise anymore, and the bodies of himself, and his friends, till loosed by him who has the keys of hell and death: or "the bars shall go down to the grave"; the members of his body, as Jarchi, which are the bars of it, as some in Bar Tzemach; the strength and support of it, as particularly the bones, these shall go down to the grave, and there turn to rottenness and dust; and therefore, as if he should say, as he elsewhere does, "what is my strength, that I should hope?" Job 6:11;
when our rest together is in the dust; which is man's original, and to which he returns, and in which the dead lie and sleep until the resurrection; and where they are at rest from all adversity and affliction of body, mind, and estate; from all the troubles and vexations occasioned by wicked men, and from all disputes, wranglings, contentions, and animosities among friends, which would be the case of Job, and his friends, when their heads were laid in the dust, and which he supposed would quickly be; and therefore it was in vain for them to feed him with hopes of outward happiness, and for him to entertain them; it best came them both to think of death and the grave as near at hand, where their controversies would be buried, and they would be good friends, and lie quietly together, and take their rest until they should awake and rise to everlasting life.

They--namely, my hopes shall be buried with me.
bars-- (Isaiah 38:10). Rather, the wastes or solitudes of the pit (sheol, the unseen world).
rest together--the rest of me and my hope is in, &c. Both expire together. The word "rest" implies that man's ceaseless hopes only rob him of rest.

They - My hopes, of which he spake in the singular number, Job 17:15, which he here changes into the plural, as is usual in these poetical books. Bars - Into the innermost parts of the pit: my hopes are dying, and will be buried in my grave. We must shortly be in the dust, under the bars of the pit, held fast there, 'till the general resurrection. All good men, if they cannot agree now will there rest together. Let the foresight of this cool the heat of all contenders, and moderate the disputers of this world.