John Gill Commentary Job 38:12

"Hast thou commanded the morning since thy days [began], [And] caused the dayspring to know its place;" — Job 38:12 (ASV)

Have you commanded the morning since your days ;
&c.] Job had lived to see many a morning, but it never was in his power to command one; he had been in such circumstances as to wish for morning light before it was, but was obliged to wait for it, could not hasten it, or cause it to spring before its time; see (Job 7:3Job 7:4) ; one of the Targums is, ``were you in the days of the first creation, and commanded the morning to be?'' he was not, God was; he was before the first morning, and commanded it into being, (Genesis 1:3–5) (Isaiah 43:13) ;

[and] caused the dayspring to know its place ;
the first spring of light or dawn of day; which though it has a different place every day in the year, as the sun ascends or descends in the signs of the Zodiac, yet it knows and observes its exact place, being taught of God.