Darach is Gaelic for "Oak tree.” Around him you can see the leaves and acorns of the tree and rectangular portals representing passage, change or transformation. The Oak is almost synonymous with strength, steadfastness and historically is associated with the sacred groves and forests of of the Druids.
The Roman Gaius Plinius Caecilius Secundus lived in Gaul during the 1st century CE and wrote that Druid priests performed all their religious rites in Oak groves, where they gathered mistletoe from the trees with a golden sickle. Dense forests of Oak covered most of Northern Europe at that time and the tree's human-like attributes of trunk/body, branches/arms, twigs/fingers, and sap/blood may explain what made them sacred and subjects of worship to the Gaelic people.
When Christianity eventually came to Ireland, Scotland and England, Christian churches were often built in Oak groves, probably because they were already recognized as places of worship. An example is Kildare, where St. Brigid founded her abbey. Kildare derives from “Cill-dara”, the Church of the Oak. This association of place between old and new religions may also explain the carved decorative and enduring interpretations of pagan nature spirits within sacred Christian spaces through time. These images are now recognized as the Green Man.