Who can number the clouds in wisdom?.... Or has such wisdom as to be able to count them when the heavens are full of them; hence they are used to denote a great multitude, Isa 55:8; or "declare" them , set forth and explain the nature of them, their matter, motion, and use; none can do this perfectly or completely.
Aben Ezra interprets it, who can make them as sapphire? in which he is followed by Mr. Broughton and others ; the sapphire is a precious stone, very clear and lucid, of a sky colour. And then the sense is, who can make a clear and serene sky, when it is cloudy?