Over the years, I have come back to this quote many, many times. I am not, by nature, a mystic in the usual sense. My training and experience has been more along the lines of raja yoga meditation and study, which places emphasis upon developing one's mind, as it is the instrument for many spiritual enterprises.
Yet the tone of this quote rings deep within, as I have also been trained that the mental disciple must re-coup aspects of his mystical self. To me, this quote is a great reminder. I think that is so because of the connection of the human heart in subtle ways to the heart of humanity, and thus to the essential "heart of the planet."
If the planet is living - as I am convinced that it is - then it must have a heart and the book Heart indicates that the human heart can come into synchrony with that planetary heart, and thus with the heart of the solar system.