John Calvin Commentary Romans 9:21

"Or hath not the potter a right over the clay, from the same lump to make one part a vessel unto honor, and another unto dishonor?" — Romans 9:21 (ASV)

Has not the worker of the clay? etc. The reason why what is formed ought not to contend with its maker is that the maker does nothing but what he has a right to do. By the word power, he means not that the maker has strength to do according to his will, but that this privilege rightly and justly belongs to him. For he does not intend to claim for God any arbitrary power except that which ought to be justly ascribed to him.

Furthermore, bear this in mind—that as the potter takes nothing away from the clay, whatever form he may give it, so God takes nothing away from man, in whatever condition he may create him. Only this is to be remembered, that God is deprived of a portion of his honor unless he is granted such authority over men as to constitute him the arbitrator of life and death.