How is eclipse related to the shadow?

Without shadow, there is no eclipse formed. A solar eclipse occurs when the earth is covered by the shadow of the moon. If we see the sun from that shadow, which was cast by the moon, the sun would visible partially or it may not be visible.  This occurs when the moon comes in between the sun and the earth. Thus shadow plays an important role in the formation of a solar eclipse.

Similarly, a lunar eclipse occurs when the shadow of the planet earth falls on the moon. Since darkness can't be seen, the part of the earth's shadow covered by the moon is also can't be seen, forming a lunar eclipse. It happens when the sun, earth, and moon aligned in the same straight line. Here also without shadow, there is no occurrence of the lunar eclipse. 

Hence shadow has an important role in the formation of the eclipse.