Allah said,

وَكَذَلِكَ نُصَرِّفُ الآيَاتِ ...

Thus We explain variously the verses...,

meaning, just as We explained the Ayat in this Surah, such as explaining Tawhid and that there is no deity worthy of worship except Allah. This is how We explain the Ayat and make them plain and clear in all circumstances, to suffice the ignorance of the ignorant; and so that the idolators and disbelievers who deny you say, `O Muhammad! You have Darasta with those who were before you from among the People of the Book and learned with them'.

... وَلِيَقُولُواْ دَرَسْتَ ...

...so that they (the disbelievers) may say: "You have Darasta (studied),''

Ibn Abbas, Mujahid, Sa`id bin Jubayr and Ad-Dahhak said similarly.

At-Tabarani narrated that `Amr bin Kaysan said that he heard Ibn Abbas saying,

"Darasta, means, `recited, argued and debated.'''

This is similar to Allah's statement about the denial and rebellion of the disbelievers,

وَقَالَ الَّذِينَ كَفَرُواْ إِنْ هَـذَا إِلاَّ إِفْكٌ افْتَرَاهُ وَأَعَانَهُ عَلَيْهِ قَوْمٌ ءَاخَرُونَ فَقَدْ جَآءُوا ظُلْماً وَزُوراً

وَقَالُواْ أَسَـطِيرُ الاٌّوَّلِينَ اكْتَتَبَهَا فَهِىَ تُمْلَى عَلَيْهِ بُكْرَةً وَأَصِيلاً

Those who disbelieve say, "This (the Qur'an) is nothing but a lie that he has invented, and others have helped him at it, so that they have produced an unjust wrong (thing) and a lie.''

And they say, "Tales of the ancients, which he has written down, and they are dictated to him morning and afternoon.'' (25:4-5)

Allah described the chief liar of the disbelievers (Al-Walid bin Al-Mughirah Al-Makhzumi),

إِنَّهُ فَكَّرَ وَقَدَّرَ

فَقُتِلَ كَيْفَ قَدَّرَ

ثُمَّ قُتِلَ كَيْفَ قَدَّرَ

ثُمَّ نَظَرَ

ثُمَّ عَبَسَ وَبَسَرَ

ثُمَّ أَدْبَرَ وَاسْتَكْبَرَ

فَقَالَ إِنْ هَـذَآ إِلاَّ سِحْرٌ يُؤْثَرُ

إِنْ هَـذَآ إِلاَّ قَوْلُ الْبَشَرِ

Verily, he thought and plotted. So let him be cursed! How he plotted! And once more let him be cursed, how he plotted! Then he thought. Then he frowned and he looked in a bad tempered way. Then he turned back and was proud. Then he said, "This is nothing but magic from that of old. This is nothing but the word of a human being!'' (74:18-25)

Allah said next,

... وَلِنُبَيِّنَهُ لِقَوْمٍ يَعْلَمُونَ ﴿١٠٥﴾

And that We may make the matter clear for the people who have knowledge.

The Ayah means, so that We explain the matter to a people who know truth, and thus follow it, and know falsehood, and thus avoid it. Allah's wisdom is perfect, He allows the disbelievers to stray, and He guides the people who have knowledge.

Allah said in other Ayat,

يُضِلُّ بِهِ كَثِيرًا وَيَهْدِي بِهِ كَثِيرًا

By it He misleads many, and many He guides thereby. (2:26)

and;

لِّيَجْعَلَ مَا يُلْقِى الشَّيْطَـنُ فِتْنَةً لِّلَّذِينَ فِى قُلُوبِهِم مَّرَضٌ وَالْقَاسِيَةِ قُلُوبُهُمْ

That He (Allah) may make what is thrown in by Shaytan a trial for those in whose hearts is a disease and whose hearts are hardened. (22:53)

and,

وَإِنَّ اللَّهَ لَهَادِ الَّذِينَ ءَامَنُواْ إِلَى صِرَطٍ مُّسْتَقِيمٍ

And verily, Allah is the Guide of those who believe, to the straight path. (22:54)

وَمَا جَعَلْنَآ أَصْحَـبَ النَّارِ إِلاَّ مَلَـئِكَةً وَمَا جَعَلْنَا عِدَّتَهُمْ إِلاَّ فِتْنَةً لِّلَّذِينَ كَفَرُواْ لِيَسْتَيْقِنَ الَّذِينَ أُوتُواْ الْكِتَـبَ وَيَزْدَادَ الَّذِينَ ءَامَنُواْ إِيمَـناً وَلاَ يَرْتَابَ الَّذِينَ أُوتُواْ الْكِتَـبَ وَالْمُؤْمِنُونَ وَلِيَقُولَ الَّذِينَ فِى قُلُوبِهِم مَّرَضٌ وَالْكَـفِرُونَ مَاذَآ أَرَادَ اللَّهُ بِهَـذَا مَثَلاً كَذَلِكَ يُضِلُّ اللَّهُ مَن يَشَآءُ وَيَهْدِى مَن يَشَآءُ وَمَا يَعْلَمُ جُنُودَ رَبِّكَ إِلاَّ هُوَ

And We have set none but angels as guardians of the Fire, and We have fixed their number only as a trial for the disbelievers, in order that the People of the Scripture may arrive at a certainty and the believers may increase in faith, and that no doubts may be left for the People of the Scripture and the believers, and that those in whose hearts is a disease (of hypocrisy) and the disbelievers may say, "What does Allah intend by this example!''

Thus Allah leads astray whom He wills and guides whom He wills. And none can know the hosts of your Lord but He. (74:31)

and;

وَنُنَزِّلُ مِنَ الْقُرْءَانِ مَا هُوَ شِفَآءٌ وَرَحْمَةٌ لِّلْمُؤْمِنِينَ وَلاَ يَزِيدُ الظَّـلِمِينَ إَلاَّ خَسَارًا

And We send down in the Qur'an that which is a healing and a mercy to the believers, and it increases the wrongdoers in nothing but loss. (17:82)

and,

قُلْ هُوَ لِلَّذِينَ ءَامَنُواْ هُدًى وَشِفَآءٌ وَالَّذِينَ لاَ يُؤْمِنُونَ فِى ءَاذَانِهِمْ وَقْرٌ وَهُوَ عَلَيْهِمْ عَمًى أُوْلَـئِكَ يُنَادَوْنَ مِن مَّكَانٍ بَعِيدٍ

Say, "It is for those who believe, a guide and a healing. And as for those who disbelieve, there is heaviness in their ears, and it is blindness for them. They are those who are called from a place far away.'' (41:44)

There are similar Ayat that testify that Allah sent down the Qur'an as guidance to those who fear Him and that He guides or misguides whom He wills by the Qur'an.