ثُمَّ أَخَذْتُ الَّذِينَ كَفَرُواThen I took hold of those who disbelieved,means, `despite all of this, they denied the Messengers and the Message they brought, so I seized them, i.e., with My punishment.'فَكَيْفَ كَانَ نَكِيرِand how terrible was My denial!means, how great and intense and terrible do you think My punishment was?And Allah knows best