It is always important to examine such questions in context. This comment is made by Arobin to Edna after she says she wants to "determine what characer of a woman I am" because she doesn't know how to answer this question. We see Edna here continuing to try and establish her own identity and make sense of who she is and who she wants to be as she seeks greater and greater independence and rebels against the traditional roles of wife and mother that society thrusts on her.
What is interesting about Arobin's response is the way that he, from this remark, threatens to merely replace these roles of mother and wife with another role that is imposed upon Edna rather than giving her space and time to decide who she wants to be for herself. Consider how he says, "I can tell you what manner of woman you are." Edna has struggled against her identity being formed as a result of a patriarchal society and here is Arobin trying to impose his will on her again to form her into something. There is an ironic tinge to this comment therefore, as it shows how Arobin is selfishly using Edna for his own purposes, and doesn't really love her in the way that would allow her to take the time to establish her own identity.