Tafsir of Ibn Kathir on the Ayats Muhkamat and the Mutashabihat

It is He Who has sent down upon you the Book, in which there are precise signs (verses) that are the mother of the Book and other ambiguous ones.
Those who have a deviation in their heart follow the ambiguous, in a spirit of discord and with the intention of interpreting it, but their interpretation is known only to Allah.
And those rooted in knowledge say, “We believe in him, all things are from our Lord.”
But only those who know how to recognize the essential reconsider.
(The Family of Imran, 3:7)

Allah declares that in the Qur’an, there are Ayats that are Muhkamat, totally clear and simple, and these are the foundations of the Book that are clear to everyone.
And there are Ayats in the Qur’an that are Mutashabihat not entirely clear to many, or some people.
Therefore those who refer to the Ayats Muhkamat to understand the Ayats Mutashabih, will have acquired the correct guidance, and vice versa.
That is the reason why Allah says:

Who are the mother of the Book (3:7)

That is, they are the basis of the Qur’an, and they should be mentioned to seek clarification, when necessary.
And he says:

And others ambiguous (3:7) since they have several meanings, some that agree with the Muhkamat and others that carry other literal indications, although these meanings may not be desired.

The Muhkamat are the Ayats who explain the rulings of abrogation, what is permitted, the prohibitions, the laws, the limits, the obligations and the decisions that must be believed and applied.
As for the Ayat Mutashabihat, they include abrogated Ayats, metaphors, oaths, and what should be believed, but not implemented.

Muhammad bin Ishaq bin Yasar commented (on: And other ambiguous ( 3:7)) saying “that they contain the proof of the Lord, immunity for the servants and a refutation of the opponents and falsehood. They cannot be changed or altered from what is their meaning.”
He also said: “As for ambiguous Ayats, they could (but should not) be altered and changed, and this is a test from Allah to the servants, just as He tested them with the things that are permitted and forbidden.
Therefore these Ayats should not be altered to imply a false or distorted meaning of the truth.”

Hence Allah says:Those who have a deviation in the heart (3:7)Referring to those who are lost and deviated from the Truth to falsehood who:Follow the ambiguous (3:7)

That is, they cite the Mutashabih, because they are able to alter their meanings to accommodate their false interpretation since the terms of the Mutashabihat cover a wide area of meanings.
As for Ayat Muhkam, they cannot be altered because they are clear and therefore constitute unequivocal evidence against the wrong people.
That is why Allah says:

In the spirit of discord (3:7)

That is, they seek to mislead their followers by pretending to prove their innovation with the Qur’an – as Ayats Mutashabih of the latter – but this is evidence against them and not in their favor.
For example, Christians (may claim that) ‘Isa is divine because the Qur’an says that he is Ruhullah and His Word, which he gave to Mary, while ignoring Allah’s statements: He is but a servant whom We favored (43:59) and Verily, Isa, before Allah, is like Adam.
He created him from earth and then said to him: Be!
And it was (3:59).

There are other Ayat who clearly state that ‘Isa is only one of the creatures of Allah and that he is the servant and Messenger of Allah, among other Messengers.And then Allah says: And with the intention of interpreting it (3:7)

To alter them as they wish.
Imam Ahmad narrated that ‘Aishah said: “The Messenger of Allah recited: It is He Who has sent down upon you the Book, in which there are precise signs (verses) that are the mother of the Book and other ambiguous ones.”
Even “those who know how to recognize the essential.”
And he said:

When you see those who argue about him (using the Mutashabihat), then they are the ones Allah was referring to.
Therefore, be aware of them.

Al-Bukhari collected a similar Hadith in the Tafseer of this Ayah (3:7) just as Muslim did in the book of Qadar (the Divine Will) in his Saheeh, and Abu Dawood in the Sunnah section of his Sunan, from A’ishah that: “The Messenger of Allah recited this Ayah”It is He Who has sent down upon you the Book, in which there are precise signs (verses) that are the mother of the Book and other ambiguous ones.”
Even “only those who know how to recognize the essential reconsider.”

Then he said:

When you see those who follow what is not so clear from the Qur’an, then they are those whom Allah described, so be careful with them.

This is the transmission collected by Al-Bukhari. Source: Tafsir of Qurtubi