The shankh is used in two ways in a puja ritual. One for blowing before the start of ritual and other for actual puja ritual. The shankh which is used for blowing should not be kept for puja.
Blowing of shankh has special significance in puja ritual. It has been mentioned in ‘Varaha Puran’ that one should not open the door of temple without first blowing the shankh. The left turned shankh is blown before the start of puja or performance of arti. There are three types of frequencies in the atmosphere namely sattva dominant, raja dominant and tama dominant. Among them the raja dominant and tama dominant frequencies generate distressing vibrations. The sattva dominant frequencies get attracted to the place of puja ritual but these frequencies are opposed by the raja and tama dominant frequencies so that they do not reach the place of puja and thus the flow of sattva frequencies is hindered.
When the shankh is blown before the start of puja energy is emitted from the shankh. This energy reduces the strength of distressing frequencies. Besides a protective armour of chaitanya (divine consciousness) is formed around the articles of puja.
There is another benefit too. That is when the shankh is blown the activated energy of Shri Vishnu in the universe gets attracted towards the place of worship which is not only beneficial to the person who is blowing the shankh but also to all those who hear it.
Just as the shankh is blown before the start of puja, it is also blown before an arti. The objective behind this being to sustain the deity’s chaitanya attracted to the place of puja ritual and the pure atmosphere generated because of the sattvik frequencies, for a long period.