Humanistic psychology seeks to deeply understand what it looks like for a person to be healthy, "whole", fully functioning - for without such a vision, the attempt to treat or heal people is doomed to lapse into blind band-aid fixes or surface-level pathologizing. The subfield is characterized by a holistic view of body/mind/spirit, a careful look at what influences hinder us from being fundamentally "all right", and a belief that every person is capable of reaching the peaks of the human experience (what Maslow, one of the pioneers of the field, termed "self-actualization" and with which he crowned the famous hierarchy of needs).
Rowan's survey is not necessarily the most readable front-to-back, but it is packed chock full of jumping-off points into more detailed and specialized writings. I do recommend at least skimming it if you're interested in topics such as peak experiences, self-actualization, societal ills and cures, the relationship between systemic oppression and mental health, growth and maturity, and generally living up to the immense potential in the human condition.