Al-An'aam 6:125

Whoever Allah wills to guide, He opens his heart to Islam; and whoever He wills to lead astray, He makes his heart tight and constricted[41], as if he were climbing up into the sky. This is how Allah punishes those who do not believe.

[41] Due to his arrogance and persistence in sin.

So whoever Allāh wants to guide - He expands his breast to [contain] Islām; and whoever He wants to send astray[342] - He makes his breast tight and constricted as though he were climbing into the sky. Thus does Allāh place defilement upon those who do not believe.

[342] As a result of the person's arrogance and persistence in sin.

125. And whomsoever Allâh wills to guide, He opens his breast to Islâm; and whomsoever He wills to send astray, He makes his breast closed and constricted, as if he is climbing up to the sky. Thus Allâh puts the wrath on those who believe not.[16]

[16] (V.6:125) If Allâh تعالى wants to do good to a person, He makes him comprehend the religion [the understanding of the Qur’ân and the Sunnah (legal ways) of the Prophet صلى الله عليه وسلم].
Narrated Mu‘âwiya رضي الله عنه in a Khuthah (religious talk): I heard Allâh’s Messenger صلى الله عليه وسلم saying, "If Allâh wants to do good to a person, He makes him comprehend the religion [the understanding of the Qur’ân and the Sunnah (legal ways) of the Prophet صلى الله عليه وسلم]. I am just a distributor, but the grant is from Allâh. (And remember) that this nation (true Muslims, real followers of Islâmic Monotheism) will remain obedient to Allâh’s Orders [i.e., following strictly Allâh’s Book (the Qur’ân) and the Prophet’s Sunnah (legal ways)] and they will not be harmed by anyone who will oppose them (going on a different path) till Allâh’s Order (Day of Judgement) is established." (Sahih Al-Bukhâri, Vol.1, Hadîth No.71).

And whomsoever it is Allah's will to guide, He expandeth his bosom unto the Surrender, and whomsoever it is His Will to send astray, He maketh his bosom close and narrow as if he were engaged in sheer ascent. Thus Allah layeth ignominy upon those who believe not.