Hast thou commanded the morning since thy days - That is, in thy lifetime hast thou ordered the light of the morning to shine, and directed its beams over the world? God appeals to this as one of the proofs of his majesty and power - and who can look upon the spreading light of the morning and be insensible to the force and beauty of the appeal? The transition from the ocean to the morning may have been partly because the light of the morning is one of the striking exhibitions of the power of God, and partly because in the creation of the world the light of the sun was made to dawn soon after the gathering together of the waters into seas; see Genesis 1:10, Genesis 1:14. The phrase “since thy days,” implies that the laws determining the rising of the sun were fixed long before the time of Job. It is asked whether this had been done since he had an existence, and whether he had an agency in effecting it - implying that it was an ancient and established ordinance long before he was born.
Caused the day-spring to know his place - The day-spring (שׁחר shachar) means the “aurora, the dawn, the morning.” The mention of its “place” here seems to be an allusion to the fact that it does not always occupy the same position. At one season of the year it appears on the equator, at another north, and at another south of it, and is constantly varying its position. Yet it always knows its place. It never fails to appear where by the long-observed laws it ought to appear. It is regular in its motions, and is evidently under the control of an intelligent Being, who has fixed the laws of its appearing.