The fence around the lake
Without the fence around the lake one could hardly notice the ice on the lake because it is covered by snow in the same way as the ground. The fence is saying: do not trespass!
The Ten Commandments are like the fence, they are saying: No!
Sometimes we rebel against the Ten Commandments because they seem to be against our freedom, they seem to us as obstacles.
When we step on the ice and sink into the icy water, then we understand the purpose of the fence, the purpose of the commandments. (MČ)