“I understand,” we say, and then we go and do something else because we do not understand anything, we do not even hear what is said.  Usually our understanding is thus, superficial and empty, because we do not hear or see what is being said.
Sometimes, however, we say, “hey, yeah, I see, I realize, I do discover,” and we do, we hear and see what is being said, and we discovered, we realizes the content of it.
There are actually two types of understanding; it is the understanding with the head and the understanding with the whole body, all through.  Between these two is a big difference.

When we understand with your head, what others say, in spoken or written words, is only phrases.  They are but beautiful words and even sensible, that we may love reading and which we quote liberally, but they are completely pointless.  It is in fact only an addition to what we already have and are.
When, however, we realize or discover something, we understand it all through, with the whole body, and immediately it is a cold fact and inseparable part of ourselves and our whole existence, that we never have to think more about. It really is we ourselves.
We do not necessarily talk about it or quote it, but if we do, then we do it in our own words in our own way, in the hope that someone realizes or discovers its contents.

Understanding all through, with all our being can only be if and when we let go of all our knowledge. We have in fact to abandon everything.  Peel of us all that we have collected for us in a long or short lifetime, until nothing is left. The new cannot be where everything is full of old stuff, ideas, opinions, phrases, quotes, etc.
It is a fact, if we hold fast to the old and tired phrases, recurring words, nothing new will happen.  It is not until we dare to let go of it all, dare to have an empty head and understand nothing, that we can realized or discover something new.

When everything is gone, we face reality, which is really nothing, and at the same time it contains everything, because where there is nothing there are all possibilities. Then we are reality, truth, life, and all possibilities.  Nothing more, nothing less.