Tafseer Al-Baqarah (2: 1)
From the Book, Introduction to the Tafseer of the Quran,
by the Ameer of Hizb ut Tahrir, Eminent Jurist and Statesman, Ata Bin Khalil Abu Al-Rashtah
(Translated)

Allah (swt) said,

[الم] “Alif Lam Mim” [TMQ Surah Al-Baqarah 2:1].

This verse, and the rest of the separated letters at the beginning of the surahs, are all from the mutashabih (ambiguous), meaning those ayaat that carry more than one meaning. As such, they require exerting some effort to interpret their meaning, i.e. to determine the most preponderant meaning. Therefore, absolute certainty is not possible with the meanings of the mutashabih; otherwise, they would be classified as muḥkam (clear and definitive).

Many opinions have come about them, with the preponderant being that they are أسماء للسور تحمل معنى التحدي للعرب “names for the surahs carrying the meaning of a challenge to the Arabs.”

As for why it is preponderant that they are names for the surahs, it is because the name for the Arab is what catches the ears and draws the sight to the named thing. If you said ‘Muhammad’ when a man walked past, the one who hears, turns to the passing man. Beginning the surahs with these separated letters catches the ears to what is being recited and turns the sight towards it.

Therefore, pronouncing [الم] “Alif Lam Mim” at the beginning of a surah in front of some people who are listening catches their ears to the surah that will be recited. In that is the meaning of a name to indicate the named thing, so that is why we said that they are names of the surahs, so we say: Surah Alif lam Mim al-Baqarah, surah Ya Sin and so on.

[Note: Among the indicators of the name in Arabic language is the definite article ال “the”, the يا “O!” of calling and the attribution (إسناد isnaad) to it. The last of these is considered to be of the most important indicators for the Arabs. It is applied here with these separated letters, as [ذَلِكَ الْكِتَابُ] “This is the book” is attributing (مسند musnad) back to [الم] “Alif Lam Mim” within the sequence

[ألم (1) ذَلِكَ الْكِتَابُ] “Alif Lam Mim (1) This is the Book.”

As for them carrying the sense of a challenge to the Arabs, it is because they touch their hearing initially with letters from their own speech. Yet, with that, they are not able to come with the like of the Quran, or even a single surah from it. Let alone the fact that the illiterate does not utter letters, instead they say, phonetically, آ إل إم, “Aa, ’l, ‘m” but they do not say ألف ميم لام “Alif Lam Mim,” alphabetically, except if they are learned. The Messenger of Allah (saw) was illiterate, and they knew him and he lived among them. All of this only increases their censure, establishes the evidence against them and is challenging them.