You may want to sear the fat as well by holding the steak on its side. Searing just one side plus the fat on the edges is usually sufficient to develop the desired appearance and flavor, but you can sear both sides, too.
When heat is applied to food, the chemicals in the food change. A lot. Heat is powerful energy. Some changes are obvious, some subtle, some invisible. The most important of these changes are the Maillard reaction and caramelization. Together they make miracles. Together they make GBD: Golden Brown and Delicious.