What is the essence of the Book of Changes?

Throughout the ages, there are countless books that study the Book of Changes, but few of them can really be called the masters of the Book of Changes. This is because 99% of people who study the Book of Changes have fixed their eyes on the 64 hexagrams, and I have repeatedly realized that the essence of the Book of Changes is actually beyond the hexagrams, with two cores, one is its philosophical thought of the unity of man and nature, and the other is to understand the meaning of the Book of Changes: simplicity, change and difficulty. If you are familiar with the mystery, one leaf will know the autumn, so the ancients said: those who are good and easy will not take it.