"The people who seem innocent are often those we should watch the most carefully."
As a member of the secret police, Leo is trained to be suspicious of everything. However, he tells Grigori, his protege, an important statement, one that will be recalled throughout various events in the story. As the novel unfolds, it is obvious that no one should be easily trusted, and that looks can fool and cause disturbing consequences. This is exactly what Leo tells Grigori, that innocent-looking people are very likely to be the most wicked or wrong.
"A man's status had become defined by how much empty space surrounded him."
This quote refers to the prejudice found in the Soviet, where high-rank and governmental people would receive so many luxuries normal citizens haven't even heard of. A man's status, in this case, became known by how big his house is to the point that it feels empty. The higher the person's status, the bigger his house, and the emptier it feels. In Leo's case, most men like him didn't have families, and so the feeling of loneliness in the vast house became inevitable.
"Love did seem to be characterised by foolhardiness."
Love is a strong feeling, and when it is real, it can make a person sacrifice his life for the person or the thing he loves. It can also make him do risky and unprecedented actions. This is foolhardiness. The person forgets about himself and focuses only on pleasing his love, even if the other one doesn't share the same feelings with the same intensity.
"(Leo) calculated that a polished version of reality might be more effective than an artificial model of perfection."
Leo realized that, in a war of propaganda, the best thing is to stick to the truth but bend it to fit the needs of the people. People will believe what looks real, even if it is a bit polished and restructured to look much better and perfect than what it is in real life. However, if you bring people and show them things that seem impossible to occur, they will never believe it, and their trust will eventually fade, and the war would be lost.
"(...) he was numb to these statistics, numb to notoriety."
This quote is a reflection of what happens to people who are at war. They become emotionless, not having the slightest sympathy for those who are dead. They are used to hearing hundreds of dead people's names every day, and most of them had at least one close person dead in the war, which made the news of a stranger's death less horrifying to hear and grief on. These soldiers and citizens and everyone who witnessed war will not react to seeing people die in front of them. They might try helping, but if they die, this is their fate, and the shock will go away in a matter of seconds.
