Aspire to be an Arahant

I remember a devout Buddhist colleague of mine who told me that he would strive to be an arahant in the next life. Now, what's an arahant, I wonder. It seems that if one goes through the Buddhist path , one is able to experience the truth to the extent of cutting of a number of the ten mental fetters , becomes a noble person who is sure of enlightenment as an Arahant within seven lives. There are in fact four stages of enlightenment in Buddhism which are Sotapanna, Sakadagami, Anagami and Arahant. Now, I just wonder why my colleague would wait another lifetime? I could not imagine a medical student putting off his housemanship in his endeavor to become a specialist!