Character Analysis
Let's face it: both of Einar's wives are really similar. Dude's got a type, that's for sure. Maria and Nadya aren't in the book very much, but both of them represent a particular religious idealism to Sig. When he's trying to make a decision, he remembers how they've lectured him on forgiveness and peace. In fact, the book even makes the connection between the two of them for us:
Faith, Hope, and Love. That was what Maria had tried to teach her children, but she had died too soon to finish their education. In some move of the hand of fate, or maybe of God, Nadya had entered their lives to finish that teaching, but still, these are lessons for which you have to provide your own answers. (37.2)
We see here that the women stand for the same beliefs. They both try to encourage Einar, Anna, and Sig to believe the Bible as they do, but for Sig, it's not so black and white—he doesn't take what these women believe at face value, because he wants to make his own call.
In a way, Maria and Nadya aren't really characterized outside of their faith. It might be because that's their entire function in the narrative. We're not supposed to get to know them as individuals, but rather, think about them as standing for a set of beliefs and ideals.