R-B-B are the roots of Rabb means to nurture or develop .That is to pass a thing through ever-new changes or stages so it gradually develops & reaches its ultimate designated destination (Raghib ) As Mother Nature passes a particle through several stages & finally changes it into a pearl while gradually nurturing it on its way (T)
This kind of nurturing is called " Raboobiyat " .
Everything in the universe is a testimony to the fact that a wonderful program is at work .Just look at a seed while traversing different stages of nurturing , reaches fruition . This is what the Allah's system of sustenance is .Allah is praiseworthy for such a system of sustenance .This system is is at work automatically in the external & internal universe ,so Quran directs to implement this system of Rabubiyyah in human's society as well. Those who establish this system are termed as Rabbaniyyoon (3/78) The latent potentialities of every member are actualized only in this system & the man is qualified for further sustenance even after physical death as life is indivisible & it goes ahead to traverse other stages of the evolution .
The sustenance of Allah continues there as well .
Universal sustenance is the ultimate aim of the Quran , that is the sustenance of the mankind regardless of caste ,color ,creed or religion. .Until such system of sustenance is is reflected in a human society , it can't be called an islamic society .This is the beginning of Quranic Teachings.