What is the author's tone in The Cross and the Switchblade by David Wilkerson?

The book is written in first person, and while it is possible for some non-fiction writers to write in that perspective with a degree of objectivity, there is the very clear sense that in this case, the author is writing from an entirely subjective point of view. As discussed above, he is writing from a clearly defined sense of purpose and mission - in other words, he isn't simply presenting facts and/or narratives and leaving interpretation of those facts and narratives up to the reader (as a more objective author might). He is, rather, presenting what he believes to be clear evidence that HIS interpretation of the facts, and of the events about which he's writing, can lead only to experiences and insight parallel to his own, and those of the teenagers with whom he works.