1. "Allah"
The proper noun "Allah" solely belongs to The Almighty God, the Truth. Anything succeeding it is regarded as an adjective describing it, while it remains a noun indicative of the True God. It combines all His Attributes, and it needs no introduction from others, whereas the other Attributes attain recognition when added thereto. "Allah" is not given to anyone other than Him, nor should it ever be used for anyone besides Him.
"Allah" is the ever-Existent, the One Who causes existence, Who maintains existence, Who creates everything that exists. Whatever He creates shall perish; He never will: "... say: `Allah!' then leave them sporting in their vain discourses" (Qura'n, 6:91).
2. "Al-Rahman"
Allah has said, "All those in the heavens and the earth will come to the Beneficent God obediently" (Qura'n, 19:93).
"Al-Rahman al-Rahim" are two of the Attributes of Allah which remind people of His mercy, of the fact that His act of affecting goodness and rewards reach whomsoever He pleases, thus warding off evil from them. "Al-Rahman" and "al-Rahim" are two concurrent Attributes of His each conveying more meanings of mercy than the other.
"Al-Rahman" is an Attribute specifically relevant to Allah; none besides Him can be called or referred to as such, whereas "al-rahim" can be applied to people: One may be described as "rahim," merciful or kind, but a human cannot be "rahman".
In the Holy Qura'n, we read: "In the Name of Allah, the Most Beneficent, the Most Merciful" (Qura'n, 1:1); "The beneficent God is firm in power" (Qura'n, 20:5). It is an Attribute demonstrating that mercy can be possible only through Him. It means "the One Who grants mercy beyond which there is no other mercy at all and the like of which does not at all exist."
Though derived from mercy, "al-Rahman" is both a noun and an adjective. Neither contradicts the other.
It is commonly known that mercy means: one's desire or power of will to bring goodness to one who is much less than him in status.
3. "Al-Rahim"
Allah, Praise and Glory to Him, has said, "Inform My servants that I am the Forgiving, the Merciful" (Qura'n, 15:49).
"Al-Rahim" is derived from "rahmah," mercy or compassion."Rahmah" implies the salvation of those who receive it from harm and loss, and their being blessed with guidance, forgiveness and sound conviction. Al-Rahim, i.e. the One Who grants rahmah, is a superlative. It is the highest derivative form of rahmah. Allah has said, "He it is Who sends His blessings on you, and (so do) His angels, so that He may bring you out of utter darkness into the light, and He is Merciful to the believers" (Qura'n, 33:43).
Al-Rahim is the One Who bestows countless blessings. Some say that this word is derived from "Rahim," and we have already come to know that the root word for it is "rahmah," that is, favours from Allah and blessings; surely His blessings cannot be counted, nor can they ever be exhausted.
The Messenger of Allah has said, "One who has no compassion towards people is deprived from Allah's Compassion." He has also said, "One who does not respect the seniors among us, nor shows compassion towards our young, nor safeguards the rights of the scholars among us, is surely none of us." Compassion among the servants of Allah is a sure path to achieving the mercy of Allah. The Messenger of Allah has said, "Be merciful unto those on earth so that those in the heavens may be merciful unto you."
