It is stated in Surah 6:12 – Say: “To who belong all that is in the heavens and on earth?” Say: “To Allah. He hath inscribed for Himself (the rule of) Mercy. That He will gather you together for the Day of Judgment, there is no doubt whatever. It is they who have lost their own souls that will not believe.
There are skeptics who say that the Quran claimed that Allah has prescribed mercy for himself as stated in the above verse at S6:12, yet they claimed He does not guide some, even though he could. They also claimed that although Allah said He is Most Merciful some verses in the Quran contradicted the claim as these two verses quoted respectively will tell as at S6:35 If their spurning is hard on thy mind, yet if thou wert able to seek a tunnel in the ground or a ladder to the skies and bring them a sign, (what good?). If it were Allah’s will, He could gather them together unto true guidance: so be not thou amongst those who are swayed by ignorance (and impatience)! And the other verse they claimed being stated is in S14:4 We sent not a messenger except (to teach) in the language of his (own) people, in order to make (things) clear to them. Now Allah leaves straying those whom He pleased and guides whom He pleases: and He is exalted in power, full of Wisdom. The example they gave to show that Allah is not that merciful is in the story of Adam and Eve how can there be mercy if both of them were not immediately forgiven just because they ate some fruits in the garden instead they were banished by Allah to other place as stated in S20:123 He said: “Get ye down, both of you, all together, from the Garden, with enmity one to another: but if, as is sure, there comes to you Guidance from Me, whosoever follows My Guidance, will not lose his way, nor fall into misery.
The problem with skeptics is that they read the Quran at random and then try to find loopholes but If one read the Quran earnestly one will certainly find there is mercy from Allah as the ultimate goal to us is the living in the garden of eternity which is prepared for those who are righteous after their sins is forgiven. And also to those whose hope is in Allah there is mercy as He is One who forgive again and again as described by the following verses of the Quran:- S15:49-50 Tell My servants that I am indeed the Oft-forgiving, Most Merciful, And that My Penalty will be indeed the most grievous Penalty. And it is stated in S40:3 Who forgive sin, accept repentance, is strict in punishment, and hath a long reach (in all things). There is no god but He: to Him is the final goal.
Nevertheless that being quoted He leaves straying whom He pleases and guide whom He pleases will depend on one own effort to be a disbeliever or to be of those who seek His guidance as defined by the following verses respectively:-
In S4:167-168 Those who reject Faith and keep off (men) from the way of Allah, have verily strayed far, far away from the Path. Those who reject Faith and do wrong, Allah will not forgive them nor guide them to anyway. That will be the consequence of those who purposely reject the signs of Allah and thus will be deprived of His guidance. However for the righteous it is different as stated in S19:76 “And Allah doth advance in guidance those who seek guidance: and the things that endure, good deeds, are best in the sight of thy Lord, as rewards, and best in respect of (their) eventual return.” This shows that those who stray went straying on their own account and those who is guided they take the guidance of Allah on their own account.
In the case of Adam and Eve there is forgiveness from Allah and the final return as stated S2:37-39 Then learnt Adam from his Lord words of inspiration, and his Lord turned towards him; for He is Oft-Returning, Most Merciful. We said: “Get ye down all from here; and if, as is sure, there comes to you Guidance from me, whosoever follows My guidance, on them shall be no fear, nor shall they grieve “But those who reject Faith and belie Our Signs, they shall be companions of the Fire; they shall abide therein.”
On the Day of Judgment the good or bad deeds one had done will be manifested as stated in S3:30 “On the Day when every soul will be confronted with all the good it has done, and all the evil it has done, it will wish there were a great distance between it and its evil. But Allah cautions you (To remember) Himself. And Allah is full of kindness to those that serve Him.” And ultimately to each is his own decision to disbelieve or to believe in Allah as to find His guidance or to stray from His path as shown in the Book the Quran which state in S76:2-3 Verily We created Man from a drop of mingled sperm, in order to try him: So We gave him (the gifts), of hearing and sight. We showed him the Way: whether he be grateful or ungrateful (rests on his will).
And He gives you of all that ye ask for. But if ye count the favors of Allah, never will ye be able to number them. Verily, man is given up to injustice and ingratitude. (Surah 14:34) “But, without doubt, I am He that forgives again and again, to those who repent, believe, and do right, who, in fine, are ready to receive true guidance.” (Surah 20:82). “But if any have done wrong and have thereafter substituted good to take the place of evil, truly, I am Oft-Forgiving, Most Merciful. (Surah 27:11)