Dostoevsky: Demons discussion

A very unexpected proposition from Nikolai to Marya is met with a disorienting rejection. It's suggested that Marya is mentally ill, but there is some uncertainty about exactly how ill she is. Nikolai prefaces his proposal with "You're not altogether mad, you know!" but seems to change his mind by the end of the encounter. She refers to Nikolai in the 3rd person, for example calling Varvara "his mother". She brings up Grishka Otrepyev ("False Dmitriy I", d. 1606 wikipedia), then identifies Nikolai as Otrepyev. Why does Nikolai offer to live with her in the mountains? He seems to think it a noble gesture, but she scorns it, saying her "bright falcon" has become a pedestrian "owl". Finally she accuses him of having unsheathed a knife, sending him into a violent rage.

It may be that Marya's madness is also of a divine nature. Perhaps she correctly perceives Nikolai's character as untrustworthy. As in 1.4 "The Lame Girl", where the narrator wonders if Shatov may be underestimating Marya, she chooses to communicate obliquely and makes few concessions to the listener. Indeed a knife is unsheathed in the very next section by Fedka the Convict.

We still perhaps don't understand why Nikolai married Marya in the first place. Based on his dialogue with Shatov in the previous chapter, it could be a perverse whim; as a nihilist, he seems bent on nothing more than violating all sense and logic. Maybe Marya's irrationality attracts him, but her spiritual sensitivity is repulsed by his essential self-centeredness.

I’m wondering to what extent Nikolai’s relationship Mary symbolizes his vacillating thoughts and feelings about religion and the church. Either way, their marriage could well have been launched as an irrational stunt.
For the fact that they had such a history together and that he was able to talk to her with an evident closeness and special understanding in the parlor the week before, this encounter in this scene seems to have ended with a sense of tragedy.