During Yajna we chant Mantras; a divine ambience builds up in the atmosphere. The sound waves create mystical and subtle vibrations in the surroundings and that has a profound effect on our mind, on the human brain.
Mantras have immense powers, known as Mantraja Siddhi. In Vihangam Yoga Yajna, we use these Mantras. We call upon the Rishis. These insightful Rishis appear in their divine zone and shower their blessings upon us. This is why we use Mantras, the Vedic Mantras. The Vedic Mantras have an amazing power. In Vedas, there are different Mantras for different wishes and we use them accordingly. Through Yajna, we develop the feeling of surrender to the creation. "Idam Na Mama" or "it is not mine" is the feeling of surrender, the feeling of sacrifice, the sense of benevolence which develops due to Yajna.
After each chanting of hymns followed by offering of ahuti in inflamed fire the word 'swaha' is pronounced. It is necessary to understand the meaning of this word 'swaha'. In 'Nirukta'(a Vedic dictionary) the word 'swaha' is described as - "Swahetyetat su aaheti" Meaning that whatever is beautiful speech/saying, is called 'swaha'. Therefore the meaning of "Swaha" is "Sukti" meaning beautiful utterance. Each Vedic hymn is a "Sukti", a beautiful utterance of a sage.