Before answering what this book "does," so to speak, perhaps it would be more advantageous to observe directly what the book "is." Through specific portraits of Victorians and their lives, the book is a depiction of human influence and legacy. Cardinal Manning, Thomas Arnold, Charlsen Gordon, and Florence Nightingale are not in a club or anything. Rather, what makes the group suitable for treatment in this book is that the effects of their actions and decisions extended way past the time of their deaths.
For instance, the story of Cardinal Manning shows that during specific moments of history, certain institutions became liable to change. When he seized the moment, he was able to change the course of the Christian church—no small feat. And yet, his ability to make change does not stem from his Christ-like aspects, but from his tenacity, his incisive use of authority, and his aggressive demeanor. In fact, he seems at times to resemble Christ not at all. Instead of being warm-hearted and open-minded, he typically treated others with contempt and was openly aggressive toward other church influencers.
This shows that underneath the specific garb of their occupation or role, important people tend to be those with strong political convictions that they pursue with vehemence. That is certainly the case with Major-General Charles Gordon. He went down in history not for working well with others or for putting the nation first. Rather, he felt a strong opinion and acted decisively, and in the end was proven correct. The brilliance of his dealings with Sudan saved Britain much trouble, even though he was a loner with fierce opinions.