They spend their days in wealth, and in a moment go down to the grave. They die, i.e.' without suffering from any prolonged or severe illness, such as that grievous affliction from which Job himself was suffering.
Probably Job does not mean to maintain all this absolutely, or as universally the case, but he wishes to force his friends to acknowledge that there are many exceptions to their universal law, that wickedness is always visited in this world with condign punishment, and he wants them to account for them exceptions (see verse 7).