In plain words
Why must we say it three times only? What does it mean?
Śānti of body, mind and spirit: all three are truly needed
Śānti of the body, Śānti of the mind, Śānti of the Ātma. So I need Śānti in all three of these. Śānti of body, of mind and of spirit: I need all three. That is why śānti śśānti śśāntiḥ: if there is no Śānti in these three, we cannot live. So: O God! Grant me Śānti in all three of these. You may have Śānti in the spiritual life, but when you do not have proper health in the body, only unrest comes there. There is Śānti in body and in spirit. But if there is no Śānti in the mind, it is of no use. So Śānti must be in all three. Prayers such as this are what the great ṛṣis, from ancient times, practised through many kinds of sādhana, experienced, rejoiced in and gave to the world. Many people, in many ways, went on doing tapas: ‘Where is God, where is He, where is He?’ But some gave up. ‘It is not within our power.’ Some others: ‘We must do still more; what has our life been given for? We must carry on the search for God, come what may’: so they held fast with determination. Those who continued with such determination came out of their tapas and said, so it is told, ‘Vedāhametaṃ puruṣaṃ mahāntaṃ ādityavarṇaṃ tamasaḥ parastāt’. We have seen God. Where did we see Him? Vedāhametaṃ puruṣaṃ mahāntaṃ ādityavarṇaṃ: God, it is said, is radiant with the light of a thousand suns. Where is He? He is beyond darkness. Only beyond it did we see God. ‘You too must see, you too must see,’ all the holy ones went on proclaiming to the world. What is this darkness? Our body itself is darkness. God is just beyond attachment to the body. This mind itself is darkness. God is just beyond this mind; that is why, body is like a water bubble, mind is like a mad monkey. Don't follow the body, don't follow the mind; follow the conscience.