Differences between the meanings of Rahman and Rahim

Differences between the meanings of Rahman and Rahim

Rahman and Rahim are both derived from the root word rahema, but involve two different dimensions of it. Rahman [mercy] is a sign of increasing, abundant mercy. Rahim is of the same essence as rahema, but it refers to and signifies permanence and constancy of mercy. We understand two things from these two words. From the word Rahman we understand that God is very merciful and the scope of His mercy is very extensive. From Rahim we understand that God’s mercy is continuous, permanent, and abiding. This mercy will never stop.

From Imam Khamenei's commentary on the first Surah of the Holy Quran, Surah Al-Fatiha
March 13, 1991