Complex sentence: Such far and wide activities would have called for symbols that remind them of the unity with the Church of the East, it is possible that the Patriarchate of Seleucia-Ctesiphon instituted the rite of the Holy Leaven to serve as one.
Split into simpler sentences: Such far and wide activities would have called for symbols that reminded them of the unity with the Church of the East. Thus it is possible that the Patriarchate of Seleucia-Ctesiphon instituted the rite of the Holy Leaven to serve as one.