Holy Leaven
This substance was divided between the apostles to be used in preparing sacramental bread ever since and successfully brought to the Christians of the East.
The earliest historical mention of the Holy Leaven is from c. 900, and tradition that connects it with the Last Supper is fairly new, dating from the 13th and 14th centuries.
It is likely that the Holy Leaven is a symbol instituted to unify congregations by the Patriarchate of Seleucia-Ctesiphon during vast missionary expansion of the Church of the East.
[7] According to this version, the Holy Leaven was taken to the Christians of the East by Thaddeus of Edessa and Saint Mari, but the other Seventy disciples of Jesus refused it, saying: "We will consecrate for ourselves whenever we wish.
After Jesus had died and was taken down from the cross and pierced with the spear, the tradition holds that John witnessed both blood and water running from the wound unmixed.
[19] According to 14th century writer Abdisho bar Berika,[2] the Holy Leaven was brought to the East by Apostles Thomas and Bartholomew as well as Thaddeus of Edessa and Saint Mari of the Seventy disciples.
Abdisho bar Berika also posits a challenge to Western Christians who do not observe the sacrament of the Holy Leaven.
"[4] The missionary activities of the Church of the East, that reached as far as India, China, and Mongolia, provide a possible background.
[23] Historically, Holy Leaven could have functioned much the same way as the Catholic fermentum,[15] a practice that may have persisted until the end of the 7th century.
[24] Although specifics about the fermentum are not known for certain,[15] it was probably pieces of Eucharistic bread carried from one Latin diocese to another and added to the sacramental wine.
[24] In a similar fashion, the addition of the Holy Leaven materially connects each Eucharist celebrated in the Assyrian Church of the East to the original Last Supper.
[25] In arguing for the validity of the Eucharist in the Liturgy of Addai and Mari, the Catholic Church viewed the sacrament of Holy Leaven as a sign of continuity of tradition going back to the Last Supper.
