Your mother is not coming; she cannot come.

This is said at the end of Part 2 and at the start of Part 3. It's said to emphasize Leopold's great disappointment. He becomes very emotional at this realization. He comes to understand his family history and the ugly realities that come along with it.

Karen . . . wanted to share with someone her pleasure in being alone: this is the paradox of any happy solitude.

In the above quote, the character Karen wants to share the experience of her solitude with someone. She has been searching for love. However, due to outside circumstances, she had been unable to marry the man she loves. She has an affair and hurts those around her. Ultimately, Karen is left alone yearning for company.

She is a woman who sells girls; she is a witch.

She acted on me like acid on a plate.

Both these quotes are in reference to Mme Fisher. She is written as the iconic evil mother. Motherhood is a central theme in the entire book. The mothers in the story are regularly referenced as ruthless and evil. Mme Fisher is even called "quasi-vampiric." Karen longs to be a "natural mother". She uses Mme fisher as the antithesis of a natural mother.

Henrietta knew of the heart as an organ; she privately saw it covered in red plush and believed that it could not break, though it might tear.

Henrietta shows she has a comprehension of the fragile nature of the heart. However, it also proves her resilience. Henrietta is the one who breaks the news to Leopold that his mother is not coming. Afterwards, she cares for him while he cries. This exemplifies her kind nature and empathetic understanding. She is acutely aware of relationships and how humans react to them.