When you bake bread, you generally want it to cool down completely before slicing into it. This is because bread is still baking, in a way, when you take it out of the oven. As it cools, the steam inside the bread is very slowly released through the crust, setting the crumb inside. If you cut into it too quickly, your piece will still be tasty, but it may be overly wet and the rest of the bread – particularly the side exposed by cutting into it – could become soggy, then stale quickly. The best way to serve bread warm is to cool it down and reheat it before serving.
I have a ceramic hot plate-type gadget similar to this Bun Warmer that does a great job of keeping bread warm for serving. You simply heat it up in the microwave or the oven, then place it into your bread basket (I typically use a large napkin in the basket to keep dinner rolls, etc. covered even further). The heat lasts for quite a while and will definitely keep heated rolls from cooling off too quickly at the table.