2:6 Certainly, those who disbelieve, it is the same to them whether you (O Muhammad) warn them, or do not warn them, they will not believe.
After explaining the characteristics of those favored by Allah through His guidance from the Qur’an, Allah now explains the disbelievers.
Kafaru means disbelieved.
Kufr means disbelief, opposite of iman or belief.
Kufr also means ingratitude, which can be used for ingratitude towards Allah or mankind.
The root word is kafara meaning covering or hiding. Those who cover are called kuffar (e.g. the cultivators of land, they covered the seeds with earth, 57:20). The disbelievers are called kaafiruun.
Ad Dahhak said this refers to Abu Jahal and 6 people from his household.
Ibn Abbas said this refers to leaders of Medinan Jews e.g. Ka’ab ibn al Ashraf, Huyayy ibn al Akhtab etc.
Ar Rabi’ ibn Anas said it refers to the leaders of idolaters who were killed at Badr.
If we are accusing someone as a disbeliever, it is only allowed after his kufr is revealed from the Unseen after his death (people can change before death).
Indifference towards Warnings
Indzar means giving some knowledge and instill fear simultaneously. This is only used to warn someone against something they already know, but urgently.
This ayah is not discouraging mukmin to invite everyone towards the straight path. It is just explaining the attribute of kafiruun i.e. they wont listen, so that the mukmin wont be disheartened when rejected.
All hearts are within Allah’s control. When someone stops listening (especially due to ego) Allah will cover his heart so it will be harder to listen next time. A man can stop listening as he has freewill as decreed by Allah. Allah has the right to cover his heart as also decreed by Allah.
Similarly, from many ahadith, whoever lets an evil act, a black dot will appear on his heart. If he does a good deed, a white dot will appear. This will go on until his heart is either black or white totally.