Travaileth with pain - That is, his sorrows are like the pains of parturition. Eliphaz means to say that he is a constant sufferer.
All his days - It seems difficult to see how they could have ever formed this universal maxim. It is certainly not literally true now; nor was it ever. But in order to convey the doctrine that the wicked would be punished in as pointed and striking a manner as possible, it was made to assume this universal form - meaning that the life of the wicked would be miserable. There is some reason to think that this and what follows to the close of the chapter, is an ancient fragment which Eliphaz rehearses as containing the sentiments of a purer age of the world.
And the number of years is hidden to the oppressor - Wemyss renders this, “and a reckoning of years is laid up for the violent.” So, also, Dr. Good. The Vulgate renders it, “and the number of the years of his tyranny is uncertain.” Rosenmuller, Cocceius, Drusius, and some others suppose that there should be understood here and repeated the clause occurring in the first hemistich, and that it means, “and in the number of years which are laid up for the violent man, he is tortured with pain.” Luther renders it, “and to a tyrant is the number of his years concealed.” It is difficult to tell what the passage means. To me, the most probable interpretation is one which I have not met with in any of the books which I have consulted, and which may be thus expressed,” the wicked man will be tormented all his days.” To one who is an oppressor or tyrant, the number of his years is hidden. He has no security of life. He cannot calculate with any certainty on its continuance. The end is hid. A righteous man may make some calculation, and can see the probable end of his days. He may expect to see an honored old age. But tyrants are so often cut down suddenly; they so frequently perish by assassination, and robbers are so often unexpectedly overcome, that there is no calculation which can be formed in respect to the termination of their course. Their end is hid. They die suddenly and disappear. This suits the connection; and the sentiment is, in the main, in accordance with facts as they occur.