Allah states that in the Qur'an, there are Ayat that are Muhkamat, entirely clear and plain, and these are the foundations of the Book which are plain for everyone. And there are Ayat in the Qur'an that are Mutashabihat not entirely clear for many, or some people. So those who refer to the Muhkam Ayat to understand the Mutashabih Ayat, will have acquired the correct guidance, and vice versa. This is why Allah said,

﴿هُنَّ أُمُّ الْكِتَـبِ﴾

(They are the foundations of the Book), meaning, they are the basis of the Qur'an, and should be referred to for clarification, when warranted,

﴿وَأُخَرُ مُتَشَـبِهَـتٌ﴾

(And others not entirely clear) as they have several meanings, some that agree with the Muhkam and some that carry other literal indications, although these meaning might not be desired.

The Muhkamat are the Ayat that explain the abrogating rulings, the allowed, prohibited, laws, limits, obligations and rulings that should be believed in and implemented. As for the Mutashabihat Ayat, they include the abrogated Ayat, parables, oaths, and what should be believed in, but not implemented.

Muhammad bin Ishaq bin Yasar commented on,

﴿مِنْهُ آيَـتٌ مُّحْكَمَـتٌ﴾

(In it are verses that are entirely clear) as "Containing proof of the Lord, immunity for the servants and a refutation of opponents and of falsehood. They cannot be changed or altered from what they were meant for.'' He also said, "As for the unclear Ayat, they can (but must not) be altered and changed, and this is a test from Allah to the servants, just as He tested them with the allowed and prohibited things. So these Ayat must not be altered to imply a false meaning or be distorted from the truth.''

Therefore, Allah said,

﴿فَأَمَّا الَّذِينَ فى قُلُوبِهِمْ زَيْغٌ﴾

(So as for those in whose hearts there is a deviation) meaning, those who are misguided and deviate from truth to falsehood,

﴿فَيَتَّبِعُونَ مَا تَشَـبَهَ مِنْهُ﴾

(they follow that which is not entirely clear thereof) meaning, they refer to the Mutashabih, because they are able to alter its meanings to conform with their false interpretation since the wordings of the Mutashabihat encompass such a wide area of meanings. As for the Muhkam Ayat, they cannot be altered because they are clear and, thus, constitute unequivocal proof against the misguided people. This is why Allah said,

﴿ابْتِغَآءَ الْفِتْنَةِ﴾

(seeking Al-Fitnah) meaning, they seek to misguide their following by pretending to prove their innovation by relying on the Qur'an -- the Mutashabih of it -- but, this is proof against and not for them. For instance, Christians might claim that ﴿`Isa is divine because﴾ the Qur'an states that he is Ruhullah and His Word, which He gave to Mary, all the while ignoring Allah's statements,

﴿إِنْ هُوَ إِلاَّ عَبْدٌ أَنْعَمْنَا عَلَيْهِ﴾

(He ﴿`Isa﴾ was not more than a servant. We granted Our favor to him.) ﴿43:59﴾, and,

﴿إِنَّ مَثَلَ عِيسَى عِندَ اللَّهِ كَمَثَلِ ءَادَمَ خَلَقَهُ مِن تُرَابٍ ثُمَّ قَالَ لَهُ كُن فَيَكُونُ ﴾

(Verily, the likeness of `Isa before Allah is the likeness of Adam. He created him from dust, then (He) said to him: "Be!'' and he was.) ﴿3:59﴾.

There are other Ayat that clearly assert that `Isa is but one of Allah's creatures and that he is the servant and Messenger of Allah, among other Messengers.

Allah's statement,

﴿وَابْتِغَآءَ تَأْوِيلِهِ﴾

(And seeking for its Ta'wil,) to alter them as they desire. Imam Ahmad recorded that `A'ishah said, "The Messenger of Allah recited,

﴿هُوَ الَّذِى أَنزَلَ عَلَيْكَ الْكِتَـبَ مِنْهُ آيَـتٌ مُّحْكَمَـتٌ هُنَّ أُمُّ الْكِتَـبِ وَأُخَرُ مُتَشَـبِهَـتٌ﴾

(It is He Who has sent down to you the Book. In it are verses that are entirely clear, they are the foundations of the Book; and others not entirely clear,), until,

﴿أُوْلُواْ الأَلْبَـبِ﴾

(Men of understanding) and he said,

«فَإِذَا رَأَيْتُمُ الَّذِين يُجَادِلُونَ فِيهِ، فَهُمُ الَّذِينَ عَنَى اللهُ، فَاحْذَرُوهُم»

(When you see those who argue in it (using the Mutashabihat), then they are those whom Allah meant. Therefore, beware of them.)''

Al-Bukhari recorded a similar Hadith in the Tafsir of this Ayah ﴿3:7﴾, as did Muslim in the book of Qadar (the Divine Will) in his Sahih, and Abu Dawud in the Sunnah section of his Sunan, from `A'ishah; "The Messenger of Allah recited this Ayah,

﴿هُوَ الَّذِى أَنزَلَ عَلَيْكَ الْكِتَـبَ مِنْهُ آيَـتٌ مُّحْكَمَـتٌ﴾

(It is He Who has sent down to you the Book. In it are verses that are entirely clear,) until,

﴿وَمَا يَذَّكَّرُ إِلاَّ أُوْلُواْ الأَلْبَـبِ﴾

(And none receive admonition except men of understanding.)

He then said,

«فَإِذَا رَأَيْتِ الَّذِينَ يَتَّبِعُونَ مَا تَشَابَهَ مِنْهُ؛ فَأُولئِكَ الَّذِينَ سَمَّى اللهُ، فَاحْذَرُوهُم»

(When you see those who follow what is not so clear of the Qur'an, then they are those whom Allah described, so beware of them.)''

This is the wording recorded by Al-Bukhari.