Marble is quite soft and porous and does need to be sealed. The counter might come sealed from the factory, but the homeowner needs to seal it every couple of years to keep it from being stained or etched. Fortunately, this is easy to do. Clean the countertop with water and a mild cleanser, and let it dry overnight. Then, use a clean white towel to saturate the stone with sealant. Make sure to follow the manufacturer's instructions.