Yasna

Yasna is the Avestan language name of Zoroastrianism's principal act of worship, and also the name of the primary liturgical collection of Avesta texts, recited during that yasna ceremony.

The function of the yasna ceremony is, very roughly described, to strengthen the orderly spiritual and material creations of Ahura Mazda against the assault of the destructive forces of Angra Mainyu. The yasna service, that is, the recitation of the Yasna texts, culminates in the apæ zaothra, the "offering to the waters." The ceremony may also be extended by recitation of the Visperad and Vendidad texts. A normal yasna ceremony, without extensions, takes about two hours when recited by an experienced priest.