You are reading a tafsir for the group of verses 40:4 to 40:6

In verse 4, it was said: مَا يُجَادِلُ فِي آيَاتِ اللَّـهِ إِلَّا الَّذِينَ كَفَرُ‌وا (No one quarrels about the verses of Allah, except those who disbelieve.). This verse declares quarreling in the matter of the Qur'an an act of kufr (disbelief). And the Holy Prophet ﷺ has said: اِنَّ جِدَالأ فِی القُراٰنِ کُفرُ (Surely, quarreling (jidal) in the Qur'an is kufr.' (Reported by al-Baghawi, al-Baihaqi in ash-Shu'ab from Sayyidna Abu Hurairah ؓ ; and reported by Abu Dawud and al-Hakim who has rated it as 'Sahib- Mazhari)

It appears in Hadith that, on a certain day, the Holy Prophet ﷺ heard two persons quarreling about some verse of the Qur'an. He got angry, and came out with his blessed face showing the signs of anger. He said, 'communities before you were ruined because they had started quarreling in the matter of the Book of Allah.' (Reported by Muslim from ` Abdullah Ibn ` Amr Ibn Shu'aib - Mazhari)

This جِدَال (jidal) declared as: کُفر (kufr) by the Qur'an, and Hadith, means throwing taunts, passing sarcastic remarks, engineering disputes over self-invented and absurd doubts, or to give such meaning of a verse of the Qur'an as is counter to other verses of the Qur'an and to the binding textual imperatives of Sunnah - something that amounts to alteration in the Qur'an. Otherwise, any honest inquiry about something ambiguous or vague, or trying to find a solution of a difficult word or expression, or to mutually investigate and discuss possibilities while deducing injunctions and rulings from the text of some verse are things not included under this jidal, in fact, it is an act of thawab (reward) in its own place (al-Qadi al-Baidawi, Qurtubi and Mazhari).

In the last sentence of verse 4, it was said: فَلَا يَغْرُ‌رْ‌كَ تَقَلُّبُهُمْ فِي الْبِلَادِ their [ prosperous ] movements in the cities should not deceive you.). The kuffar (disbelievers) from the tribe of Quraish used to travel to Yemen during winter and to Syria in summer with their trading caravans. They were held in esteem all over Arabia because of their services to Baytullah at Makkah, therefore, they remained safe during their travels and profited from their commercial ventures. This was the backbone of their wealth and territorial power. That this state of affairs with them kept continuing despite the challenge from Islam and the Holy Prophet ﷺ was a matter of pride for them - 'Had we been the culprits in the sight of Allah, all these blessings would have been taken away from us!' This situation could have made even some Muslims easy victims of doubt. Therefore, in this verse, it was said that Allah Ta’ ala had granted them a temporary respite in His wisdom and under His expedient consideration. So, let Muslims not be deceived by this leash given to them. Once this period of respite is over, they are going to be visited by a punishment, and this territorial power of theirs is going to be taken away from them. This started from the Battle of Badr, and up to the Conquest of Makkah, the foreboding manifested itself fully and conclusively within a span of six years.