What is Reuven's father saying when he tells his son, "I learned that a blink of an eye in itself is nothing. But the eye that blinks, that is something."

Even out of context of the book, one can tell that Reuven's father is trying to teach Reuven a life lesson.  The blink of an eye is typically a very short period of time during which nothing much can seem to happen.  Yet, the eye that blinks represents the person behind the eye and indeed, people are what we should all pay attention to.  Perhaps Reuven's father is trying to emphasize the importance of people first and foremost.