A commitment is a public pledge to do something. A commitment may be as mundane as a promise to clean your room, or it may be as dramatic as General Douglas McArthur's famous line, "I shall return," when he was driven from the Philippines by the Japanese early in World War II. At either extreme, or anywhere in between, a commitment is one of the most powerful motivators of human performance.
Most college professors simply assume that students are committed to doing their best. This is another difference in style from high school. If you don't want to go to class, don't go. If you don't want to do your home work, don't do it. More generally, if you want to waste your time and money, your professors want nothing to do with you. So long as you do nothing that interferes with the serious students, you can do just about anything you want. And just about the easiest thing to do is to take advantage of this free style approach to education and let your studies slide. That is why it is helpful to make a commitment.
Making a commitment does not mean dedicating yourself to your studies. A dedicated person has a single goal in life, such as making an Olympic team or being elected to Congress. Dedicated people have a one-track mind; everything else is secondary to their paramount mission in life. Of course, one can be a true scholar and dedicate oneself to learning. But such a strong commitment is not necessary. In fact, good commitment should be almost certainly attainable. It is much better to commit yourself to "getting at least a C" than to fail at "getting an A." Always make your commitment at a level that is challenging but that you believe diligent effort will produce.
You may not have noticed that I defined a commitment as being a public pledge. Evidence indicates that private commitments, such as New Year's Resolutions, are much less likely to be fulfilled than ones that somehow involve another person. It is therefore important to announce your commitment as a student to someone else and to back your commitment up in a meaningful way.