I am unsure how this book could be taken as substance other than a deeper Christian walk with Jesus Messiah.
There is what's referred to as the beholding principle; meaning, you become what you behold. One can never, NEVER, improve oneself by looking inward. It is impossible. If you want to become more patient, you look at the One who is most patient. If you want to become more loving, you look upon the fountain of love Himself, Jesus.
As Molinos puts it, "One of the healthiest things you can do in order to learn to walk in the inward way (and to lose yourself) is to look up on reason and "sound logic" as something that is created. The most reasonable conduct you can perform is to discard a great deal of your reasoning. Believe God."
And, further, "You will know that you are far from perfection if you do not find everything in God. Know that pure, perfect love consists of these elements: the Cross and denial of yourself. These elements are totally voluntary...There is a great difference between doing and of suffering and dying. Doing is delightful. It belongs to beginners in Christ. Suffering belongs to those who are seeking. Dying - dying to the self - belongs to those who are being completed in Christ."
Oh, if only I had more room to quote from this man. Only with the correct paradigm of the God-man Jesus who is Bridegroom, King, and Judge will this book make sense. Is it Gospel? No, but Molinos received and lived revelation about Jesus that speaks volumes even today.
Without this worldview, you are left merely to look at oneself and that is a hapless place to be...
Lastly, after 'searching inside this book', there appear to be updated versions available. I currently own a version from the SeedSowers Christian Books Publishing House, Volume 5 of the Library of Spiritual Classics. I would recommend purchasing the book found here on amazon - it's been cleaned up a bit :-) The Spiritual Guide (Library of Spiritual Classics)
Cheers