The opa osun (also called opa orere or opa osungaga) is used by Yoruba babalawos (diviners) as a symbol of office but also as an altar to the divination god Orunmila (also called Ifa, 'the grand priest and custodian of the Ifa Oracle', i.e. the Orisha of wisdom, knowledge and divination).
The staff is used as a walking stick by babalawos during ceremonies honouring Orunmila (including the Itefa Ifa initiation ceremony). During Orunmila ceremonies, the babalawo leads the procession through the village carrying his opa osun, to let the staff fall is to invite the wrath of Orunmila. As such the babalawo must ensure that the staff remains erect in order to receive full blessings from the god.
Blood sacrifices are made to the staff as an altar to Orunmila. The sacrifices are believed to replenish the babalawos abilities and power (ase) to prevent death and overcome other destructive forces. When not in use, the staff is stuck into the ground in front of the babalawo’s house (and by an akoko tree) to protect the babalawo while he sleeps.