Question: The Qur'an al-karim says, "Allah guides whomever He wills, and He leaves to stray whomever He wills." Since it is Allah who leaves to stray a person, is it proper for Him to put aberrant people in Hell?
There are other Qur'anic verses that clarify this verse. Just as hadith-i sharifs clarify the Qur'an al-karim, so some verses clarify some other verses.
Similarly, some la-madhhabi people [people who do not follow any of the four madhhabs], in order to deny the four of the six fundamentals of faith, focus on a single verse and say, "Aha, it is written herein that fundamentals of faith (iman) are two." Thus, they disregard other Qur'anic verses. They, for example, direct their attention to the 62nd verse of Surah al-Baqarah and claim that all Jews and Christians who believe in only Allah and the next world will go to Paradise. However, it is written in the books of tafsir that what is meant in this verse by "the people entering Paradise" is Musawis who believed in Hadrat Musa in his time and Isawis who believed in Hadrat Isa in his time.
As is seen, la-madhhabi people focus on a single verse and, so to say, conceal the verses commanding us to believe in all holy books and prophets. How can a person who disbelieves the Qur'an al-karim and rejects the Last Prophet enter Paradise? That such a person will stay in Hell eternally is clearly stated by other verses in the Qur'an al-karim.
The heretical sect called the Jabriyyah focuses on the Qur'anic verse mentioned in the question above and says, "Allah guides whomever He wills, and He makes whomever He wills a disbeliever. It is only He who compels humans to do good deeds or to commit sins. Humans do not play a role in them."
On the other hand, the Mu'tazilite sect maintains quite the contrary, saying, "Allah does not guide anyone. He does not interfere in these affairs." Both positions are wrong. The Qur'anic verse mentioned in the question above declares explicitly that the view of the Mu'tazilite sect is wrong. Also, the following Qur'anic verses expose the wrongness of the views of the Jabriyyah:
(Whoever does an atom's weight of good or evil will receive the requital for it.) [Az-Zilzal 7, 8]
(Let him who wishes believe, and let him who wishes deny.) [Al-Kahf 29]
If Allahu ta'ala forced humans to do evil or good, He would not have stated, "Whoever does an atom's weight of good or evil will receive the requital for it." As for the issues of faith and guidance, if it were Allahu ta'ala who gave faith to one against one's will or who made one disbelieve the religion by force, He would not have stated, "Let him who wishes believe, and let him who wishes deny." The first line of the following couplet is an answer to the Mu'tazilite sect. [It says that] nothing happens unless Allahu ta'ala wills it to. The second line is an answer to the Jabriyyah. [It says that] He does not do anything to a human against his will unless he deserves it.
No disaster befalls man unless Allah writes it;
He doesn't send disaster unless he deserves it.
Now we will write the explanations given for the verse mentioned in the question as well as for the above-mentioned ones. It is declared in the last two verses that humans will do good or evil deeds by their free will and receive the reward or punishment in return for them. As to the verse written in the question above, it says that it is Allahu ta'ala who does these deeds. Even though everybody does good or evil by his own free will, it is Allahu ta'ala who gives him the power to do it. For instance, there are, say, two planes, one heading for Paradise and the other for Hell. The One who makes them is Allahu ta'ala. "This plane goes to Hell," is written on one of the plane, and "This plane goes to Hell" is written on the other. It is Allahu ta'ala who takes these planes to Paradise and Hell, but humans embark them by their own will. No one is forced to get on. So no one has the right to say to Allahu ta'ala, "If you had not flown that plane to Hell, we would not have boarded it."
The summary of these two verses is as follows:
(I will put those who believe and do good deeds in Paradise, and I will put those who disbelieve and do evil deeds in Hell.)
As is seen, man believes and does righteous deeds by his free will and choice. However, it is Allah who gives this power to him. In addition to it, He accepts his faith and acts of worship. It is again Allah who gives the power to disbelieve to a person who disbelieves by his own free will and choice.
Allahu ta'ala has clearly informed humans about the deeds that will lead them to Paradise or Hell. So there is no excuse, no pretext left for them. A disbeliever will not be able to say, "If I had known, I would have believed so and done such good deeds."