This passage is like stated in the introduction, "Short and sweet". Within one paragraph, Pai-Chang manages to explain one of the most complicated and difficult to understand concepts. After reading this a few times I have managed to gain a slight understanding of what he is trying to explain. I think what he is saying is that the mind is perfect as is, its only our perception of it and its abilities that are clouded. Enlightenment seems like it isn't a change in what one's mind consists of but merely the clarity of seeing what it really is. Every one's mind is the same, they are all originally perfect, the difference between an ordinary person and a sage is that the sage lacks delusion and sees things clearly. It is like saying that we are equipped with all that we could ever need from the very start, it is just a matter of understanding that, that allows us to behold the Buddha nature.