The supposed contradiction claim is as follows:
Allah does NOT forgive shirk:
Allah forgiveth not that partners should be set up with Him; but He forgiveth anything else, to whom He pleaseth; to set up partners with Allah is to devise a sin most heinous indeed. -- Sura 4:48
Allah forgiveth not (the sin of) joining other gods with Him; but He forgiveth whom He pleaseth other sins than this: one who joins other gods with Allah, Hath strayed far, far away (from the right). -- Sura 4:116
Apparently this verse contradicts:
Allah forgives shirk (even in the same sura):
... Yet they [the Israelites] worshipped the calf even after Clear Signs had come to them; even so We forgave them; and gave Moses manifest proofs of authority. -- Sura 4:153
So therefore the person is arguing one verse says Allah does not forgive shirk, yet he forgave the children of Israel for committing shirk, so which one is it?
The argument only exposes the ignorance of the non-Muslims, because had they bothered to use their brain they could have solved this one for themselves, but since they are biased they decide that they shall not use their brains and that they will play dumb, so therefore I will have to use my brain for them.
When the Quran says that Allah does not forgive shirk, this means that if you die and meet Allah on judgement day without repenting from this major sin while you were alive Allah would never forgive you, however so if you commit shirk and repent of it while you are alive Allah will forgive it, the verses are referring to the AFTER-LIFE. Allah will never forgive a person who has died and has not repented of shirk, this is very easy to understand, and if someone wasn't bias they would easily see that. In fact I went to check the tafsir of Ibn kathir and it also agrees! :
Allah said that He,
[لاَ يَغْفِرُ أَن يُشْرَكَ بِهِ]
(forgives not that partners should be set up with Him (in worship),) meaning, He does not forgive a servant if he meets Him while he is associating partners with Him,
[وَيَغْفِرُ مَا دُونَ ذَلِكَ]
(but He forgives except that) of sins,
[لِمَن يَشَآءُ]
(to whom He wills) of His servants. Imam Ahmad recorded that Abu Dharr said that the Messenger of Allah said,
«إِنَّ اللهَ يَقُولُ: يَا عَبْدِي مَا عَبَدْتَنِي وَرَجَوْتَنِي، فَإِنِّي غَافِرٌ لَكَ عَلى مَا كَانَ فِيكَ، يَا عَبْدِي إِنَّكَ إِنْ لَقِيتَنِي بِقُرَابِ الْأَرْضِ خَطِيئَةً مَا لَمْ تُشْرِكْ بِي، لَقِيتُكَ بِقُرَابِهَا مَغْفِرَة»
(Allah said, "O My servant! As long as you worship and beg Me, I will forgive you, no matter your shortcomings. O My servant! If you meet Me with the earth's fill of sin, yet you do not associate any partners with Me, I will meet you with its fill of forgiveness.'') Only Ahmad recorded this Hadith with this chain of narration. Imam Ahmad recorded that Abu Dharr said, "I came to the Messenger of Allah and he said,
«مَا مِنْ عَبْدٍ قَالَ: لَا إِلهَ إِلَّا اللهُ ثُمَّ مَاتَ عَلَى ذَلِكَ، إِلَّا دَخَلَ الْجَنَّة»
قلت:وإن زنى وإن سرق؟ قال:
«وَإِنْ زَنَى وَإِنْ سَرَق»
. قلت: وإن زنى وإن سرق؟ قال:
«وَإِنْ زَنَى وَإِنْ سَرَقَ ثَلَاثًا»
، ثم قال في الرابعة:
«عَلَى رَغْمِ أَنْفِ أَبِي ذَر»
("No servant proclaims,`There is no deity worthy of worship except Allah,' and dies on that belief, but will enter Paradise.'' I said, "Even if he committed adultery and theft'' He said, "Even if he committed adultery and theft.'' I asked again, "Even if he committed adultery and theft'' He said, "Even if he committed adultery and theft.'' The fourth time, he said, "Even if Abu Dharr's nose was put in the dust.'') Abu Dharr departed while pulling his Izar and saying, "Even if Abu Dharr's nose was put in the dust.'' Ever since that happened, Abu Dharr used to narrate the Hadith and then comment, "Even if Abu Dharr's nose was put in dust.'' The Two Sahihs recorded this Hadith Al-Bazzar recorded that Ibn `Umar said, "We used to refrain from begging (Allah) for forgiveness for those who commit major sins until we heard our Prophet reciting,
[إِنَّ اللَّهَ لاَ يَغْفِرُ أَن يُشْرَكَ بِهِ وَيَغْفِرُ مَا دُونَ ذَلِكَ لِمَن يَشَآءُ]
(Verily, Allah forgives not that partners should be set up with Him (in worship), but He forgives except that (anything else) to whom He wills;), and his saying,
«أَخَّرْتُ شَفَاعَتِي لِأَهْلِ الْكَبَائِرِ مِنْ أُمَّتِي يَوْمَ الْقِيَامَة»
(I have reserved my intercession on the Day of Resurrection for those among my Ummah who commit major sins.)'' Allah's statement,
[وَمَن يُشْرِكْ بِاللَّهِ فَقَدِ افْتَرَى إِثْماً عَظِيماً]
(and whoever sets up partners with Allah in worship, he has indeed invented a tremendous sin.) is similar to His statement,
[إِنَّ الشِّرْكَ لَظُلْمٌ عَظِيمٌ]
(Verily, joining others in worship with Allah is a great Zulm (wrong) indeed.) In the Two Sahihs, it is recorded that Ibn Mas`ud said, "I said, `O Messenger of Allah! Which is the greatest sin' He said,
«أَنْ تَجْعَلَ للهِ نِدًّا وَهُوَ خَلَقَك»
(To make a rival with Allah, while He Alone created you.)''
So as you can clearly see, the verses regarding Allah not forgiving people of shirk is referring to the here-after, that if you die in a state of shirk you will never be forgiven no matter what, you must repent of this sin before you die in order to ever be forgiven, if you do not, then you shall never be forgiven and you will be thrown into the pits of hell.
So the children of Israel were forgiven because they repented WHILE THEY WERE ALIVE, hence Allah forgave them.
So therefore there is no contradiction whatsoever, all that is evident is that the anti-Islamics are very ignorant of the Quran and Islam in general, this is perhaps the easiest supposed ?contradiction' that I have had to reply to!
And Allah Knows Best!