With every fleeting breath they cover the immensity of space, and at every moment traverse the kingdoms of the visible and the invisible....
...

By the term "clouds" is meant those things that are contrary to the ways and desires of men.

Even as He hath revealed in the verse already quoted: "As oft as an Apostle cometh unto you with that which your souls desire not, ye swell with pride, accusing some of being impostors and slaying others." [Qur'an 2:87.] These "clouds" signify, in one sense, the annulment of laws, the abrogation of former Dispensations, the repeal of rituals and customs current amongst men, the exalting of the illiterate faithful above the learned opposers of the Faith.

In another sense, they mean the appearance of that immortal Beauty in the image of mortal man, with such human limitations as eating and drinking, poverty and riches, glory and abasement, sleeping and waking, and such other things as cast doubt in the minds of men, and cause them to turn away.

All such veils are symbolically referred to as "clouds." These are the "clouds" that cause the heavens of the knowledge and understanding of all that dwell on earth to be cloven asunder.
Even as He hath revealed: "On that day shall the heaven be cloven by the clouds." [Qur'an 25:25].