Tafsir of Sad 38:10

"Or do they possess the dominion of the heavens and the earth and whatever is between them?"

This is an elaboration on what preceded—meaning: Do they actually possess the dominion of these celestial bodies and terrestrial forms, such that they would speak regarding divine affairs and exercise authority over the godly decrees which the Lord of Might and Majesty reserves for Himself?

As for His saying: "Then let them ascend through the means [of access]," this is the response to a conditional [clause] that is omitted. It implies: If they possess the mentioned dominion, then let them ascend the stairways and paths by which one reaches the heavens, so that they may govern them and dispose of affairs within them. For they have no path to governing or disposing of them other than that. Or, if they claim such dominion, let them ascend and dispose of matters so that their claim might be thought truthful; for they have no sign of its truthfulness, so the least [they could do] is to provide this as a sign.

Al-Zamakhshari and his followers said: Meaning, let them ascend the stairways and paths by which one reaches the Throne, until they are seated upon it to govern the affairs of the world and the kingdom of God Almighty, and [until they can] send down revelation to whomever they choose and deem fit. This is appropriate for the context, though it contains some delicacy. Regardless, the command for them to do so is a sarcasm directed at them, which is not hidden.

The sabab (means/cause) originally refers to a connector, like a rope or the like. Mujahid narrated that al-asbab here refers to the gates of the heavens. It has also been said that it refers to the heavens themselves, because God Almighty made them ordinary causes for terrestrial events.