King Lear - Edgar plays many roles throughout the play and performs a wide range of functions. What is the purpose of his role playing?

After reading King Lear and studying the role of Edgar at some length, it is hard not to be disappointed with the outcome of Edgar's role. He performs so many roles and functions that he seems to just be a 'plot device'. Not much time was spent by Shakespeare on establishing Edgar's qualities and virtues prior to starting him off on his journey of role playing. Through this role playing it is possible to detect …

…and strength. When he speaks of his journey through the play as a 'pilgrimage' (Act 5 Scene 3) we understand the serious sense of purpose behind Edgar's role-playing. Surely he has proved himself many times over? We may be left with many 'ifs', 'buts' besides the many recurring questions marks (?) about this complex character. But intrinsically we all agree that Edgar was a good person with the sole intention of redeeming his father, himself, King and Country.