Sedreh is a white cotton shirt which is the external symbol of being a Zoroastrian.
It reminds us to stay clean, pure and healthy in and out,in our mind and body.
In Avesta,Sedreh is called Vohumana- vastra which means a good and pure mind costume.
Sedreh has a small pocket in the front which is called the pocket of action.it reminds us that we should practice the good deeds everyday.
Koshti is a woven string made off of wool. when we are praying we wrap It around our waist 3 time which reminds us of good thoughts ,good words,and good deeds. At the second and third round we place two nodes on the string. This is to remind us that in order to protect our world and keep it in peace and balance we need to take a good care of four essential elements, air,fire,water,and soil.
Koshti has 72 threaths representing 72 sections of Avesta/Yasna.