Whenever one is chanting a mantra in Sanskrit, it can be observed that the mantra always begins with ‘Om’ and ends with˜Swaha’. This particular alignment of words has a specific meaning to it, which is elaborated in the Dharma Shastra.
According to the scriptures, Om is considered to be the ekaakshar Brahma, which means the creator and destructor of Nature. Therefore, ‘Om’ seems to be the ruler of the three properties which make up the world, according to the scriptures. Om is also seen as a symbol of Lord Ganesha, as when starting a prayer, it is Lord Ganesha who is remembered first.
The significance of Swahaa comes out of a myth from Hindu mythology. Once, there was a shortage of food for Devas, and they approached Brahma to solve their problem. Brahma converted the offering made to the fire in yajnas into food for Deva but it didn’t burn in Agni, thereby not being available to Devas. To resolve this, Brahma meditated upon Moola Prakriti and a Goddess appeared and asked what de desired. Brahma requested the Goddess to co-exist with Agni so that the offerings could be burned. He declared that it was only when the offering is made with the mantras ending in the Goddess name can it reach Devas. Incidentally, that Goddess was called Swaha.Why Every Mantra Starts With an Om and Ends With a Swaha? by