The acorn is a symbol of strength and power. In the fall, these tiny yet hardy little nuggets drop from the oak trees to land on the ground. Most will be eaten by passing wildlife, but a few will survive to form a new tree in the spring. Because the acorn only appears on a fully mature oak, it is often considered a symbol of the patience needed to attain goals over long periods of time. It represents perseverance and hard work.
In many cultures the oak is sacred, and is often connected to legends of deities who interact with mortals. Throughout history, most of the major civilizations of Europe held the oak as a highly venerated tree, and it was associated with deities in many pantheons. The Celts, Romans, Greeks and Teutonic tribes all had legends connected to the mighty oak tree. Typically, the oak was related to deities that had control over thunder, lightning, and storms.
In Norse legend, Thor found shelter from a violent storm by sitting under a mighty oak tree. Today, people in some Nordic countries believe that acorns on the windowsill will protect a house from being hit by lightning. In parts of Great Britain, young ladies followed a custom of wearing an acorn on a string around their neck. It was believed that this was a talisman against premature aging.
The Druids are believed to have held rituals in oak groves, and certainly mistletoe was to be found on oak trees. According to legend, mistletoe was indicative of the a god stopping by via a lightning strike on the tree. Certainly, oak trees seem to be more susceptible to lightning strikes than other trees, although this could be because it's often the tallest tree around.
Rulers often wore crowns of oak leaves, as a symbol of their connection to the divine. After all, if one were a living god, personification of the god on earth, one had to look the part. Roman generals were presented with oak crowns upon returning victorious from battle, and the oak leaf is still used as a symbol of leadership in the military today.
Around the reign of King Henry VIII, oak became popular for its use in construction of homes for the wealthy. Managed oak forests in Scotland supplied thousands of pieces of timber for use in London and other English cities. The bark was used as well, to create a dye that was used in ink-making.
For information on how to find the best acorns to plant an oak tree, read Collecting and Planting Acorns.