Chapters 17, 18 and 19 are elaborated upon in this lecture of the book by Shaykh Yasir Qadhi.
Chapter 17 deals with the topic of intercession. Here various topics are discussed such as the descriptions of rejected and affirmed intercession, the "Greatest Intercession" being the intercession of the Prophet ﷺ, description of what the Prophet ﷺ will do on the Day of Judgement and how he will not begin by making intercession but will prostrate and when he is given permission he will intercede, the blessed and the happiest of people who will be blessed with the intercession of the Prophet ﷺ, failure of intercession who committed Shirk and much more.
Chapter 18 deals with the topic of how Allah guides whom He wills. Here we are acquainted with numerous topics among which are explanations of many verses such as : "Verily, you (O Muhammad) guide not whom you like, but Allah guides whom He wills. And He knows best those who are the guided ones." (28:56) ,the eagerness and intense desire of the Prophet ﷺ to convert his uncle to Islam, the harmful influence that evil companions can have on people, the harm of over praising ancestors and important personalities, how the arguments of falsifiers are the arguments of Jahiliyyah and much more.
Chapter 19 deals with the topic - Excessive Dogma in the Righteous Persons is the Root Cause of Infidelity of Mankind and its deviation from True Religion. Here the topics brought to the fore deal with the explanation of the verse in Surah Nuh (71:23), how human nature towards the truth weakens in the heart while falsehood increases, confirmation of the sayings of righteous predecessors that heresy (Bid'ah) is the main cause leading to Kufr (disbelief) , excess and exaggeration (in the righteous ones) is prohibited, and knowledge of what it leads to, the harm of seclusion at the grave even with the intention of performing a righteous deed, the prohibition against statues and the wisdom in destroying them and many more such points.