The four-leaf clover (or Trifolium repens L. white clover) is an uncommon variation of the three-leaf clover, aka shamrock.
According to tradition, finding a four-leaf clover will bring good luck to their finders. Each leaf represents something special: the first leaf is for hope, the second is for faith, the third is for love, and the fourth is for luck.
The history of the four-leaf clover is unknown. But according to legend, Eve carried a four-leaf clover from the Garden of Eden. In Irish legend, St. Patrick used the shamrock’s three leaves to teach the pagans about Christianity. It symbolized the Holy Trinity, with each leaf representing the Father, Son, and Holy Ghost. When it’s found with the additional fourth leaf, it represents God’s grace.
In European history, the Celtic dominance once extended across Ireland and much of Western Europe. It was the Druids (Celtic priests) who elevated four-leaf clovers to the status of Celtic charms, allegedly potent against malevolent spirits. Their status as Celtic charms is the origin of the modern belief in their power to bestow good luck.
Throughout history, four-leaf clovers have been thought to bring luck, mostly because they are so rare. The four-leaf clover is a universally-accepted symbol of good luck.
The four-leaf clover is the best known lucky symbol around the world and across many different cultures. It is the most common yet the rarest to find. On average, there are 100,000 three-leaf clovers for every instance of a true four-leaf clover.
(The preceding information was provided by www.fourleafclovergoodluckcharms.com)