What is the importance of Brian's photographs in the novel, Ask Again, Yes?

The three photographs Brisn Stanhope keeps in his police cap depict the people that he cares for most in the world: His wife, his son and his brother. When he dies, he stipulates in his will that these photographs be sent to Francis Gleeson, his first partner as a cop. Francis is able to explain the significance of the photographs to the members of both families. He explains the sweat stains came from where Brian kept the photos and that he looked at them when he was having a rough day. The photographs bring the characters together and help them find closure.