The All-Merciful (ٱلرَّحْمـٰنِ) is on the pattern of فَعْلان from الرحمة, and the Most Merciful (ٱلرَّحِيمِ) is on the pattern of فعيل. The pattern فعلان indicates upon occurrence and renewal in the same manner as the attributes thirsty, hungry and angry, and it does not indicate upon permanence. The description also informs of the attribute’s fullness.
It came in the Tafseer of al Al-Qaeem: “Don’t you see that those who say angry [غضبان], for those who are full of anger and regret, confused, drunk and worried for those who are full with that.”1
The form فعيل indicates upon the permanence of the attribute, such as tall, beautiful and ugly or change of the attribute to that which draws near to permanence such as orator, eloquent and noble.
So the verse came with the two attributes that indicate upon Allah’s established and renewing attributes of mercy. If He (swt) had described Himself with رحيم only, then this permanent attribute of His would have occurred in the mind, but there may come a time that He will not be merciful like the noble and the orator.
If He (swt) said رحمٰن only, then it may be thought that this is a non-permanent attribute like anger and thirst. This attribute will change, such as the anger which goes and the thirst which disappears. Therefore with Al-Rahma, He combined between the two in order to indicate upon His permanent and renewed attribute Al-Rahma. Therefore, His mercy is lasting and does not cease. It is from the best combination between the two attributes. The description with one of the two does not convey what it conveys when they are combined.
The occurrence of these attributes after the word Al-Rabb, is the best position. This is because this Lord, which there is no lord other than Him, and the Master which there no is master except Him, is compassionate with His servants. Therefore the souls of the servants become happy, and their hope becomes strong by His compassion. There is also in it an indication that the Sustainer (المربّي) is necessary to be adorned with compassion, and that He is not necessary to be harsh upon whom he sustains and guides. Also, that in it is an indication to the fact that the compassion necessitates the attribute of the Rabb with all that it carries of meanings.
Therefore, the Owner (المالك) is obliged to be merciful with what he owns and who he owns, and the Sustainer (المربّي) is obliged to be merciful, and the Master (السيد) is obliged to be merciful and the Repairer (المصلح) is obliged to be merciful, and the Maintainer (القيّم) is obliged to be merciful. So the compassion necessitates that the attribute of Rabb be with all its meanings. Allah described His messenger ﷺ with compassion, while He (swt) is the greatest caretaker and greatest repairer. He (swt) said:
لَقَد جاءَكُم رَسولٌ مِن أَنفُسِكُم عَزيزٌ عَلَيهِ ما عَنِتُّم حَريصٌ عَلَيكُم بِالمُؤمِنينَ رَءوفٌ رَحيمٌ
A Messenger has come to you from among yourselves. Your suffering is distressing to him; he is deeply concerned for you; he is gentle and merciful to the believers.