How did the Psychosocial approache help us further our understanding of this concept?

I am using Eriksons's and Marcia theorys, I would like opinons and discussions on how did their theorys help us understand the concept of identity? I know I could say that both their theorys are concerned with the bodily aspect o identity, ie old age or disabilities, people with disabilities, and how this may have helped them gain embodiment for themselves through campaigning etc....but I would like to have some more examples from Erikson and Marcia theorys, especially Marcia work on adolescence's. Discuss please.