The Iruminsul, an oak or wooden pillar, was a religious symbol of the Saxon people. We know that during the Bronze age the Irminsul was found on carvings usually with some sort of sacrifice. Very often a god was carved directly into the column. In this particular one, Odin is carved onto the center.
The Scandinavian equivalent to the Irminsul is the world tree or Yggdrasil. Both symbols represent the cosmic pillar that supports the heavens and connect the worlds. It is safe to assume that both of these columns were erected for rituals to send and receive energy via sacrifice.