The letter, and the packet of notes

The house is being packed — trunks in the hall, newspapers on the floor, string sent for twice — when Karenin's messenger arrives with a thick envelope. A packet of new notes falls out. Anna reads the end first, then the whole, and knows a worse misfortune has come than any she expected: he treats her words as unsaid and gives her exactly what she wished that morning. He is in the right, he is always in the right, he is a Christian and magnanimous, and no one but she knows how for eight years he smothered everything alive in her and never once thought her a live woman in need of love. If he had killed her or Vronsky she could have forgiven it. The line about what awaits her and her son she reads as a threat, made by a man who despises her love for the boy and knows she cannot give him up. She resolves to break the web of lies and knows she has not the strength, and weeps like a punished child. She answers, 'I have received your letter. — A.', keeps the carriage, and goes to Betsy's to find Vronsky.

Getting what she wanted that morning is the worst thing that could have happened, and Tolstoy states the mechanism plainly: her position in Society is dear to her, and she cannot become stronger than herself. The forgiveness she says she could have given for a murder is the standard by which she keeps convicting Karenin of being reasonable. Her five-word reply is the last authority she has left.