Ar Rahman

I was learning abt some group of Arabic words yang cannot accept tanwin. Normally if the nouns does not contains Alif Lam, it must has tanwin at the end to indicate it an indefinite nouns. Unless it a female name or non Arab origin name. And for adjective, it will follow the nouns. So if nouns tu ada tanwin, it must have tanwin also except some group. One of the group ada lah "Kaslanu - lazy", "jau`aanu - hungry", "`aatshaanu - thirsty" ,"ghadbaanu - angry".... So my teacher then said, all the words under this group has same characteristic.. A bit hard to shows here but if you get the arabic spell, you can see it has first huruf adalah fathah - baris atas, second "sukun - tanda mati", third "fathah - baris atas" then alif and then nun with dammah - "baris depan".  And all words under this group adalah benda yang x kekal. Mcm lapar, kita x lapar selalu or x thirsty selalu or x malas selalu. And Ar Rahman pun fall under this catergories. Rahman means  merciful - pemurah. So if we bring the characteristic huruf yang seumpama dgnya, means Rahman ni is Allah maha pemurah but it not something that forever. People normally relate Ar Rahman with duniawi while Ar Rahim which something forever is for the believer only. So if you ever wonder why people yang jahat dpt benda yang best2 is because Allah is Ar Rahman to everyone .. but it wont last. So don't be sad.. Let try to be a believer so that we can get Ar Rahim.