One philosopher thought that to understand everything would mean to forgive everything. That has some interesting implications for the theory of law! Other people believe that understanding leads to the ability to control. Although both of these ideas cover part of the idea, I do not think that either of those extremes cover the possibilities fully.
To understand something means that this something becomes part of your frame of reference. Understanding builds a comprehensive web of connections.
In a practical sense, to understand
means that you are able to use or see the use of what you understand. A partial
understanding of a utensil will naturally limit your use of it. You will only
be able to use something to the extent that you understand the nature of the
utensil. A better understanding of the utensil will refine your use of it.
For example, a stick is a stick; it is useful for bashing things, or supporting something. Discover the possibility of carving wood and you have multiplied the possible applications of a stick by a million times. Not only can you refine your joints, or add nasty points to make the business of killing your prey more convenient, but you can represent things, tell people who you are. Discover paint and the wood stops rotting. Anyway, you can probably see what I mean now: Understanding builds a web of useful connections.
To understand something fully, demands that you
understand it within the context of everything else. You must understand its
role not only with reference to you but with reference to that of which you are
a part: between the thing and our environment as a whole.
Understanding discovers relationships of use between all
sorts of things. The more complete the understanding the more one can
appreciate the relationship between yourself and the thing you are using.
Let me use another example. The development of technology over the last 400 years has brought us an equal share of good things and bad. One of the bad things technology has brought us is the fact that we have allowed the use of that technology to destroy the environment. Much of that destruction was caused by an incomplete understanding of the monster we had created. But, strangely enough, as a result of our misuse of the environment we have also come to understand that same environment better, more completely. We are now more aware of what the environment means to us, more aware of how important it is to us and of how much we are part of the environment. As a result of this we are slowly developing a technology which will be more in harmony with the environment. We are even beginning to use technology to address the damage that that earlier technology and our use of it brought on. What a paradox! The interesting result is that thinking people everywhere are seeing their connection to the world in a very different and unexpected light. They feel part of something larger.
 Blaise Pascal: Tous comprendre c’est tous pardonner.