Spiritually a single column has the same significance as a tower, a structure to enable us to reach the heavens or the Divine. It may be an object of worship or a memorial. A column of light denotes an awareness of spirit or spiritual energy. Boaz (strength) and Joachim (beauty) are the two columns which stood at the entrance to King Solomons temple in Jerusalem. Single columns could represent strength or single mindedness. Two stone columns in the distance indicate a doorway to the future or a way into the unknown. It is also structural or emotional support. You might like to consult the entry for Pillar for further clarification.