What is the history behind naming fraternities and sororities using two or three greek letters?

"Eta Beta Gamma", "Alpha Gamma Pi", etc...





Why greek? Why letters? Why greek letters? How did it start? Why is it continued?

What is the history behind naming fraternities and sororities using two or three greek letters?
According to Wikipedia:





"The Phi Beta Kappa Society was formed as a forum to discuss topics not covered in the regimented classical education of universities of the era, lending the name literary fraternity to its type. Most students were well-versed in Greek, Latin, and Hebrew; Phi, Beta, and Kappa were the initials of a secret Greek motto, Philosophia Biou Kybern膿t膿s = "Love of learning [is] the guide of life". In addition to its secrecy and selection of a Greek name, it also introduced a code of high ideals, secret rituals and handclasps, membership badges, and oaths that characterized later Greek letter societies."