Characterization refers to creation of characters and giving them certain personal traits.
It is through characterization we as readers understand how people interact, how one's personal traits influences others or causes trouble and if people can change if they possess bad behaviours or attitudes.
Let's take Remi as an example. We learn towards the end of the play that Remi thinks he is superior to others maybe due to his level education. It is through Jane that we learn this trait of Remi. At the end of the play, we are not suprised to find the commotion that resulted after his speech and the death of Thoni. It resulted from how he addressed the villagers and what she said about Thoni. He said that he won't accept to be controlled by a wan which wasn't the case. At the end of the play, he regrets how he addressed Thoni.
Again, we are not surprised by Thoni's decision to commit suicide although we are saddened that she decided to carry out the activity. At a tender age, Thoni had longed the darkness she felt while she was young. She appears as kind, polite, respectful, faithful but a troubled woman. We might not know why she desired to be dead at that young age but how she felt inferior contributed to her ending her own life.
Therefore, the personal traits or qualities of the characters assist us to understand why they behave the way they behave and the ramifications of their behaviors towards others and society at large.