And the mention in His saying, 'So when the horn is blown,' is for the purpose of causation. It is as if He said: Be patient with their harm. Before them is a difficult day in which they will face the consequences of their harm, and you will face the consequences of your patience with them. The 'so' in 'So that' is for the recompense. If you say: By what does 'when' become an accusative? And how is it correct for 'that day' to be an adverbial modifier for a difficult day? I say: 'When' is in the accusative due to what is indicated by the recompense, because the meaning is: So when the horn is blown, the matter becomes difficult for the disbelievers. What allows 'that day' to be an adverbial modifier for a difficult day is that the meaning is: So that is the time of the blowing, the occurrence of a difficult day, because the Day of Resurrection comes and occurs when the horn is blown. There is a difference of opinion on whether it is the first blast or the second. It is possible that 'that day' is in the nominative case, replacing 'so that,' and 'a difficult day' is the predicate, as if it were said: So the day of the blowing is a difficult day. If you say: What is the benefit of His saying 'not easy' when 'difficult' is sufficient? I say: When He said 'upon the disbelievers,' and restricted the difficulty to them, He said: 'not easy' to indicate that it will not be easy for them as it is for the believers, to combine the warning for the disbelievers with an increase in their anger and the glad tidings for the believers and their consolation. It is also possible that it means it is difficult with no hope of it becoming easy, as one hopes for the easing of difficulties in worldly matters.