﴾إن الذين كفروا سواء عليهم ءأنذرتهم أم لم تنذرهم لا يؤمنون﴿

Indeed, it is the same to those who [kafarū (singular. kafara)] “disbelieve” whether you warn them or do not warn them, they will not “believe”.

(Qur’ān 2:6)

Qāḍī Ibn ^cAtiyyah al-Andalūsī, may Allāh have mercy on him, writes the following about this verse:

“The mental concept of kufr is derived from the [Arab’s] statement kafara [used] when something was covered or concealed; from this you get the poet Labīd ibn Rabi’ah’s statement:

في ليلة كفر النجوم غمامها

“On a night, [in which] its clouds kafara the stars (i.e. concealed them).”

…Due to this the night is called a kāfir because it covers everything with its blackness.

[It is also] due to this that farmers are called kuffār [pl. of kāfir], because they cover the seed.

Therefore, “kufr” with respect to the dīn means: he/she covered their heart with filth as a substitute for īmān, or they covered the truth with their statements and actions.”

Source: al-Muḥarrar al-Wajīz of Ibn ^cAtiyyah al-Andalūsī. Dār al-Kutub al-^cIlmiyyah. 1:87