what does he mean by that?

Regina isn't a romantic interest, but she does encourage Obama to define himself as an African-American. She encourages himself to find out who he is inside..... to find about about his history, culture, and to apply these things to his own life. Regina's love for her family and heritage are alluring..... desireable, and through Rgina and what she stood for, Obama found his inner voice again.

“Her voice evoked a vision of black life in all its possibility, a vision that filled me with longing – a longing for place, and a fixed and definite history.”