Andrew Murray, who died in 1917, was a great man in his day, a leader of the Keswick Movement of Christian spirituality, and a leader in the Dutch Reformed Church of South Africa. This book is not his best.
His counsel to the Christian reader in this book is to regard sickness as a divine judgment and healing as an opportunity for exercising faith. Faith must be exercised without "remedies" (meaning medicine and medical treatment) in order to make clear the supernatural nature of the eventual healing. There are numerous problems with this approach but lots of people seem to be drawn to it.
My advice: read the Bible. Notice how God uses "means" in the healing of Hezekiah, Timothy, and people in the Gospels. Take note of the blind man in John 9 who neither sinned nor did his parents. Surely Murray would, if living today, not spurn medical treatment. I hope so. His other books are so much better.