Before mistletoe became an excuse to kiss people at Christmas parties, it was an important symbol in ancient Celtic religion.
Pliny the Elder describes a ceremony in which Druids climbed an oak tree to harvest mistletoe with a golden sickle. Wrote Pliny:
They believe that mistletoe given in drink will impart fertility to any animal that is barren and that it is an antidote to all poisons.
Mistletoe figures in the story of the Norse god Baldur. (Also spelled Balder and Baldr.)
Baldur was the most beloved of the Norse gods. All the gods loved him except Loki the mean-spirited troublemaker.
Baldur’s mother Freya dreamed that he died and was taken by Hel. Norsemen who died in battle were taken by the Valkyries to Valhalla. Everyone else went to Hel’s kingdom. When Freya woke she went to Hel and begged her not to take her son. Hel said that if she could persuade everything in the world not to harm Baldur, he could go on living. Freya extracted an oath from rocks, elves, giants, plants, and everything else. Every thing and every creature swore not to harm Baldur. Unfortunately, Freya neglected to speak to the mistletoe. It was so small and insignificant that she didn’t see how it could be a threat to anyone.
When it became evident that nothing would kill Baldur, the other gods made a game of throwing weapons at him. Loki found out about the unsworn mistletoe. He went to the plant and took a cutting back to Asgard. He fastened it to an arrow and gave it to Baldur’s blind brother Hoder. Loki guided Hoder’s hand and the mistletoe on the arrow pierced Baldur’s heart, killing him.
There’s more to Baldur’s story, but this is the part about the mistletoe.