How do we reconcile the fact that Allah's command is between "Kaf" and "Nun" with the creation of the heavens and the earth in seven days? And why was the "earth" mentioned in the singular, even though it consists of seven layers?

Scholars have mentioned wisdoms behind the creation of the heavens and the earth in six days, despite Allah's ability to create them in an instant. Among these wisdoms are: that on each day, an event occurs which the angels magnify; that the deliberation in preparing what was created for Adam and his progeny is more profound in magnifying him; that while hastening demonstrates power more profoundly, deliberation is more profound in wisdom; to teach servants deliberation; and that the gradualness in creation dispels the notion of its occurrence by nature or by chance. It has also been said that the wisdom is to teach servants calmness and slowness in matters.