All natural stones are porous.  You might even consider them as hard sponges: they are strong and durable, but they are capable of absorbing liquids, even dissolved salts and other minerals.  Granite is one of the denser natural stones, but it still takes in liquid.  The ability of a natural stone to absorb liquids compromises its structure.  This is why stone sealing is required.

Stone sealing

Stone sealing is the process of applying a surface treatment to the natural stone to prevent staining.  As the name suggests; the application seals off the stone from liquids and other elements to avoid stains from marking the surface.  By sealing, one can prolong the stone’s usefulness and longevity.  The stone penetrating sealer to be used on granite counter tops must be that which is recommended by the manufacturer.  It is important to follow the instructions for the application of the stone penetrating sealer for better results.