Why Sura Ar-Rahman starts with the divine attribute of "Ar-Rahman"?

The following are brief extracts of the interpretation of the first few Quranic verses of Surah Ar-Rahman from Tafheem Al-Quran by Sayyid Abul A’la Moududi. It touches on the topic as to why Sura Ar-Rahman starts with the divine attribute of "Ar-Rahman"?
Verse 2 interpretation of Surah Ar-Rahman

To begin the discourse with this sentence is meant, first of aII, to tell that the Prophet Muhammad (upon whom be Allah’s peace and blessings) himself is not its author, but its Teacher is AIlah Almighty. Furthermore, there is another object also to which the word Rahman (Merciful) is pointing. If the purpose was only to say that that teaching is from Allah, and not the production of the Prophet’s mind, there was no need to use an attribute of AIIah instead of His proper name, as for that purpose any attribute from among the Divine attributes could have been adopted, But when, instead of saying that AIIah, or the Creator, or the Providence, has taught this, it was said: ‘The Merciful (Ar-Rahman) has taught this Qur’an,’ it by itself gave the meaning that the revelation of the Qur’an for the guidance of mankind was nothing but Allah’s mercy and grace. As He is most kind and Merciful to His creation, He did not like that He should leave them wandering in the darkness, and His mercy demanded that He should send down this Quran to (give) them the knowledge on which depends their right guidance and conduct in the world and their success and well-being in the Hereafter,"
Verse 3 interpretation of Surah Ar-Rahman

In other words, as Allah is the Creator of man, and it is the Creator’s responsibility to provide guidance to His creation and show it the way by following which it may fulfil the object of its erection, the revelation of this Qur’anic teaching from Allah is not only the demand of Allah’s mercifulness but also the necessary and natural demand of His being the Creator. Who else would provide guidance to the creation if not the Creator? And if the Creator did not provide guidance, who else could? And what greater defect could there be for a creator that he should not teach his creation the method of fulfilling the object, for which it has been created?
Verse 4 interpretation of Surah Ar-Rahman

One meaning of the word bayan, as used in the original, is the expressing of one’s own mind, i e. speaking and expressing one’s thoughts and intentions. Its other meaning is to make distinction between things, which here signifies the distinction between good and evil, virtue and vice.

[Soruce: Extracts from the verse interpretations of Tafheem Al-Quran by Sayyid Abul A’la Moududi]