I read this book, Mystic Christianity, about 30 years ago when I was just a teen about 17 years old. I had a yearning in my heart for the knowledge of the great masters, probably something that continued on from my previous birth.
This book was one of 3 Yogi Ramacharaka books that helped me to obtain more knowledge of the truths of the occult masters and great yogis of India. The truths of reincarnation and mysticism -- and even diet, as most true occultist and yogis are vegetarians. Vegetarian diet is expounded upon in the Bhagavad-gita by Lord Krishna (3,000 B.C.).
The book Mystic Christianity explained many of the truths of Christ that were originally part of the Catholic church, in which I was raised, but had been done away with as heresy -- such as reincarnation. "ye must be born again" is always taken by certain so-called Christians to simply mean that one has to experience a re-birth of religous consciousness. But actually, Jesus was speaking more in terms of reincarnation. For only after many lives does a person evolve upwards to the Truth. The Truth is One as God is One -- there cannot be 2 or 3 truths or gods. The truth may come guised in the garb of different religions but the underlying seed of each religion is Truth.
Later, I found the path which was right for me. It is called Vaishnavism, and simply put, it is the worship of Vishnu or Krishna. My spiritual master told me that Christ is the Greek variation of the name of God, Krishna. God has many names according to His different past-times and according to His appearance in different regions of the world: Krishna, Jehovah, Allah, Buddha, Govinda, Christ, Hari, Vasudeva - these are just a few of the millions of names of God.
He is unlimited with unlimited number of souls residing with Him in the spiritual world. Yet, some fanatics will make proclamations that He has only one name and only one son. Even an ordinary man has more than one name and one son.
I recommend reading both Mystic Christianity and the Bhagavad-gita As It Is for starters. And then you can proceed to the many books of spiritual knowledge which are available today, translations made available to us by many of God's representatives, some who have gone on to the eternal spiritual realm finishing their term of existence within this material realm.