Why do we understand so little of what we read? I can suggest one reason. Most of us read more novels than anything else when we were young. Some of us still do. You know how we read novels. Some of us read them in a day, others in a week. Later in life a few of us re-read one or two of them. That is apt to remain our idea of 'reading', our habit, our technique. And that is why our books are so wordy, why what can be said in ten pages is said in two hundred.
Do we read the Masters like that? From cover to cover, and then put them away? What? You re-read the Diamond Sutra again not so long ago? Did you? And Huang Po also? How well you must know them now! But may I point out to you that when you have read any of them at intervals for the thirtieth time, and not necessarily from cover to cover, you will have understood more of them each time - and the thirty-first time most of all.
A man can read through a book and not fully comprehend one idea that is expressed therein. Or he can, to all intents, find himself within the mind that was dictating the text to his fingers. How often are readers nearer the latter extreme than the former?