To understand this question better we must look to the probable origins of such rods. The practice in question seems to derive from an ancient Roman practice set within the context of Roman law; here a ceremonial rod/staff was used as a means of transmitting judgements of punishment, vengeance or also freedom from slavery ("manumisso vindicta"). In this latter instance the former slave was tapped with the rod before the praetor and the slave was thereby freed.
It is here within this latter usage denoting freedom from slavery that we can begin to better gain an insight into the practice of the use of the "virgula poenitentiara" or penitential wand, in the Roman Christian tradition.
This penitential rod was use in a similar way by select ecclesiastical "penitentiaries" who were seated much like a Roman praetor on a seat of honour, given authority by proxy (which the rod represented) to absolve sins usually reserved to the pope or other members of the hierarchy, or (in more recent centuries) to grant indulgences on behalf of that authority. That practice is shown here in this rare photo taken during the Holy Year in 1950; the virgula wielded by the Major Penitentiary. Nicola Cardinal Canali, in St. Peter's Basilica in Rome where he is about to tap one of the pilgrims on the head with the 'wand' thereby granting the indulgence:
The chair from which the virgula poenitentiara was used, sat upon by the Major Penitentiary in St. Peter's Basilica |