Why should we say “om shaanti” thrice?

Almost every prayer uttered by a Hindu ends with the chant of ‘Om Shaanti’ three times. ‘Om’ is the supreme name of God, Shaanti means quelling or subjugation of undesirable calamities. There are three possible impediments –
Natural (Aadhilaukika) - such as floods, draughts etc
Mental (Adhyaatmika) - such as pain, stress etc
Material (Aadhibhautika) - caused by fellowmen, animals etc., To ward away the three kinds of impediments by the grace of Supreme God, we chant “Om Shaanti” thrice.
Hindu worship is also marked by the prayer for universal peace – ‘sarve janaaha sukhino bhavantu’ meaning “may everyone in the universe be peaceful and healthy”.