Comment on the first monologue of Medea?
The monologue by Medea establishes her side of the story. We learn prior to this that Jason has left her to marry the princess and that Medea is angry and sad over this turn of events. The Chorus initially tries to tell Medea to be calm and basically says that these kinds of things happen.
Once Medea starts to speak, she justifies her attitude toward Jason and situation she now finds herself in. She explains that she is a foreigner in a strange land because of all she did for Jason. She expresses frustration over the subservient role of women society and the powerlessness they have in marriage, stating the best a woman can hope for is to "manage him who shares the bed with her." She reminds the chorus that women are the ones who bear the pain of childbirth, and she reminds these women that while Corinth is their home and they have their family connections there, is does not have that comfort.
By the time she has laid out all of her woes, many of which the Chorus would share, she directly states that she must pay Jason back for what he has done to her. The Chorus is wholly with her at this point -- she is a very convincing speaker!