Why is it important to chant mantras loudly?
It is believed that during a yagya the gods come down and grant the wishes of a person performing the yagya. The power of Vedic and yagya mantras is such that the gods become helpless and are persuaded to come down. When mantras are ceremoniously chanted and offerings made, powerful vibrations are generated. These dispel feelings of hatred, dishonesty, impropriety, selfishness and other negative actions amongst those present, resulting in the elimination of many problems, worries and fears.
It is believed that in an environment dominated by the sound of Vedic mantras, children are blessed with noble qualities and thoughts. Wherever there is a divine influence, good people emerge, endowed with love, goodwill, honesty and good thoughts.
Religious texts describe several kinds of yagyas. Besides daily yagya, there is provision for special kinds too. Thousands, hundreds of thousands or more mantras may be chanted at the yagya. Eventually the blessing is attained. The sound of mantras being chanted, combined with the power of the resolve made by the person performing the yagya, reaches the divine power that converts the chants into the desired blessing.
Once Maharaja Prathu resolved to perform hundred Ashvamedh yagyas. After he had completed 99 yagyas and was already feeling the beneficial effects, Lord Indra felt demoralised and was worried about losing his kingdom. During the hundredth yagya, Indra changed form and took away the horse in order to create an obstacle. However, Prathu's son forcibly had the horse released.