What is the sin of those whom Allah does not wish to guide, as stated in the noble verse: "Not upon you is their guidance, but Allah guides whom He wills"?

The will of Allah is coupled with His justice and wisdom. So, whomsoever He wills, He guides by His grace and mercy, and whomsoever He wills, He leads astray by His justice and wisdom. The misguidance of a servant is due to his deeds and what his hands have earned, as in His (Allah’s) saying, "And We will turn their hearts and their eyesight away, just as they did not believe in it the first time, and We will leave them in their transgression, wandering blindly" (Al-An'am: 110), and His saying, "So when they deviated, Allah caused their hearts to deviate" (As-Saff: 5). The group upon whom misguidance became due took devils as allies instead of Allah.