Bruno understands a great deal of insight into Maria and her character through their conversation. Bruno understands that Maria is more than simply a maid, “with a life and history all of her own.” Bruno recognizes and validates her own experiences.
For as long as he has lived, Bruno has understood that Maria was there to tend to his needs. Her function was to be there for him. Due to this, Bruno understands Maria in a very limited manner. As Gretel indicates, “She’s the maid...that’s what she’s here for.” To a certain extent, Bruno sees Maria in this light. However, in hearing her narrative and story, Bruno recognizes that Maria has an experience that transcends the limited way in which he saw her. Bruno sees Maria as whole human being. Bruno is able to recognize that people are more than what they seem. This humanistic approach to individuals is something that he carries with him throughout the narrative. It is seen when he hears Maria's story and history.
Bruno is able to gain a greater understanding and appreciation about his father, as well. It increases the complexity of emotions that Bruno has towards him. On one hand, Bruno still resents his father for the family's move to "Out- With." This decision still compels Bruno to refer to his father as "stupid father." Yet, in hearing about his kindness to Maria and the benevolence with which he treated her, Bruno understands that his father is a complex individual. This also reflects the complexity that Bruno has towards his father. There is a challenge in reconciling Bruno's emotions about his father and the move to "Out- With" to what Bruno hears about his father from Maria. Similar to how Bruno's understanding about Maria has increased, Bruno recognizes that his father cannot be seen as merely something simplistic or reductive. Maria's revelation about her past and the role Bruno's father played in it is reflective of the complex nature of human beings that Bruno carries with him. Throughout the narrative, Bruno sees more than social caricatures. He recognizes the layered complexity that exists within human beings. This is an element that Bruno gains in seeking to understand his father from Maria's narrative and revelation.
I would say in a nutshell, Bruno understands that Maria is a human being. She is not an extension of his needs, but a fully formed person with her own past, needs, wants and desires.
You could say in some regards, this is also what Maria's insight into her past helps Bruno see about his own father. This is a common part of development in adolescents, as they learn to accept their parents and other family members as individuals and not just as part of their lives.
There is some more info on the Bruno/Maria relationship in the source link provided below.