Complex sentence: Pächt writes that Netherlandish painting is as distinctive as Greek sculpture, and is easily identifiable from only a small fragment, because the concept of light and shadow, hitherto not present and never seen in illuminated manuscripts was introduced by Hubert and Jan van Eyck.
Split into simpler sentences: Pächt writes that Netherlandish painting is as distinctive as Greek sculpture and is easily identifiable from only a small fragment, because of its unique characteristics. The concept of light and shadow, hitherto not present and never seen in illuminated manuscripts, was introduced by Hubert and Jan van Eyck.