The long liturgy is the ritual par excellence of the Mazdean community, and probably the foundation of its identity. This complex ceremony has several variants, the most basic of which is what we call Yasna, and a more solemn Yašt ī Wisperad. Based on the solemn variant, more complex ceremonies are also celebrated: the Widēwdād ceremony and the Wištāsp Yašt ceremony, in which a few texts are interspersed among the central texts of the ceremony, written in an older language than the rest of the liturgy. There are also parts of the ceremony that change according to the day of celebration, the deity to whom it is dedicated or the purpose of the ceremony. However, only the daily liturgy has been published. For the others, only partial editions exist, which, unfortunately, are not sufficient to reconstruct the liturgy in all its variety, as it was celebrated from the 13th to the 17th century. What's more, the liturgical manuscripts include not only the recitatives in the Avestic language, but also the ritual instructions (in Pehlevi, Pāzand or Gujarati) essential for learning about the ceremony, and which have never been published either.
The reasons for this are to be found in the history of Avestic studies and editions of Avestic texts, all of which were produced in the second half of the 19th century. For the first editors of the Avesta, Spiegel and Westergaard, the Avestic texts were not liturgical texts, even if some of them were eventually used ritually. Consequently, they consider that the original manuscripts are not the liturgical texts with ritual instructions, but the exegetical manuscripts containing the Avestic recitative with a translation of the latter into Pehlevi. Such an analysis has turned the original situation on its head, since we now know that the original manuscripts are indeed the liturgical manuscripts, from which the exegetical manuscripts are extracted. The exegetical manuscripts only show the complete text for the daily liturgy. For the rest of the variants, the exegetical manuscripts include only those sections that needed translation because they do not appear in the daily liturgy. These are the fragments included in modern editions.
For the authors of the late 19th century, such as Darmesteter and Geldner, the author of the canonical edition of the Avestian texts up to the present day, the situation was more complicated: the publication of the Pehlevi texts describing the Sassanian Great Avesta made it clear that the Avestian texts we have are not identical to the Sassanian Great Avesta. It was recognized that our texts were the recitatives of a liturgy that already existed in Sassanid times. However, this had no impact on Geldner's edition, which was already almost complete by this time. During the 20th century, until the publication of Prof. Kellens' article in the Asian Journal in 1998, this finding was ignored and the ritual use of the Avestic texts of the long liturgy was considered secondary.