Albert Barnes Commentary Job 36:12

"But if they hearken not, they shall perish by the sword, And they shall die without knowledge." — Job 36:12 (ASV)

But if they obey not - If those who are afflicted do not turn to God and yield obedience to Him, they must expect that He will continue their calamities until they are cut off.

They shall perish by the sword - Margin, as in Hebrew pass away. The word rendered “sword” (שׁלח shelach) properly means anything sent—such as a spear or an arrow, a missile—and then an instrument of war in general. It may be applied to any weapon that is used to produce death. The idea here is that the man who was afflicted because of the sins he had committed, and who did not repent of them and turn to God, would be cut off.

God would not withdraw His hand unless the afflicted person acknowledged his offenses. As God had undertaken the work of discipline, He could not consistently withdraw it, for that would, in fact, be yielding the point to the one whom He chastised. This may be the case now, and the statement made here by Elihu may involve a principle that will explain the cause of the death of many people, even of the professedly pious. They are devoted to gain or amusement; they seek the honors of the world for their families or themselves, and, in fact, they make no advances in piety and are doing nothing for the cause of religion.

God lays His hand upon them at first gently. They lose their health or a part of their property. But the discipline is not effectual.

He then lays His hand on them with more severity and takes from them an endeared child. Still, all is ineffectual. The sorrow of the affliction passes away, and they mingle again in the frivolous and busy scenes of life, as worldly as ever, and exert no influence in favor of religion.

Another blow is necessary, and blow after blow is struck; but nothing overcomes their worldliness, nothing makes them devotedly and sincerely useful, and it becomes necessary to remove them from the world.

They shall die without knowledge - That is, without any true knowledge of the plans and government of God, or of the reasons why He brought these afflictions upon them. In all their sufferings they never saw the design. They complained, and murmured, and charged God with severity, but they never understood that the affliction was intended for their own benefit.