Then He said to them, "Take heed what you hear. With the same measure you use, it will be measured to you; and to you who hear, more will be given.
For whoever has, to him more will be given; but whoever does not have, even what he has will be taken away from him."
Mark 4:23-25 (NKJV)
One thing that I notice, on almost every flight I take, is that when the safety instructions are given, most people don't pay attention. Normally, I will pay attention to the flight attendants during this time, if for no other reason than to be respectful and polite while they do their job. The flight safety instructions are for the benefit of those of us on the airplane, and it is important information that is being given, which could actually mean the difference between life or death in some situations, so it is good to pay attention to what is being said.
When we read about Jesus and His ministry in the Gospel accounts of Matthew, Mark, Luke, and John, we see that Jesus did a lot of teaching. There were a lot of people who heard what Jesus said, but not everyone benefited from His teaching, a prime example of this would be the Pharisees and the Sadducees. Because these people heard, but were not really listening to what was said, they did not get what they should have from Jesus' teaching. What they heard was right, but how they heard was not so good.
What we hear and how we hear is important. We need to pay attention to God's Word when we hear it, and be careful that we don't make the mistake of looking at the Word like it is trivial, because we have heard it before, we think we already know it, or we think that what we are hearing does not really apply to us. When we have the opportunity to hear God's Word, whether we are reading it for ourselves or we are in church or some other meeting, we need to have open, and receptive, ears to hear the Word and receive the Word.