What is meant by the impermissibility of interpreting the Qur’an based on personal opinion?

A commentator follows one of two approaches to interpret the verses of the Holy Quran:

The First Approach: "Interpretation based on Tradition (Tafsir bi al-Ma'thur)", which relies on the following sources of interpretation: 1. Interpretation of the Quran by the Quran: Where the Quran explains parts of itself, which can be either explicit and must be followed, or based on the interpreter's ijtihad (independent reasoning). 2. Interpretation by the Prophet (peace be upon him): Because he is the expounder of the Quran, and what is authentically narrated from him regarding interpretation must be adhered to. 3. Interpretation narrated from the Companions: Because it was either taken from the Prophet (peace be upon him), or their ijtihad is given precedence due to their knowledge and their witnessing of the occasions of revelation (asbab al-nuzul). 4. Interpretation narrated from the Tabi'un (Successors): This is resorted to when there is no interpretation found in the previous sources, and it is considered valid if they agree. However, if they differ, their statements are considered without the necessity of adoption.

The Second Approach: "Interpretation by Opinion or Ijtihad (Tafsir bi al-Ra'y or bi al-Ijtihad)", which is the independent reasoning of an interpreter knowledgeable in the rules of interpretation, while adhering to certain controls: 1. Reliance on what is transmitted from the Messenger and the Companions. 2. Familiarity with the rules and styles of the Arabic language. 3. Comprehensive knowledge of Islamic law (Sharia).

There are types of blameworthy interpretation by opinion that are impermissible: 1. When someone who is not academically qualified undertakes the interpretation. 2. When the interpreter follows his whims or supports his innovations, such as distorting words from their proper meanings or disregarding the fundamentals of language and Sharia. It is forbidden for the interpreter to attribute to Allah what he does not know.