Lectionary confusion
Yesterday I was greatly confused over the Sunday Gospel reading. According to the OCA web site:
27th SUNDAY AFTER PENTECOST — Tone 2 (10th of Luke). Monk Martyr and Confessor Stephen the New of Mt. St. Auxentius, Martyrs Basil, Stephen, two Gregories, John, Andrew, Peter, Anna, and many others (767). Martyr Irenarchus and Seven Women Martyrs at Sebaste (303). Bl. Theodore, Archbishop of Rostov (1394). Martyrs Timothy and Theodore—Bishops; Peter, John, Sergius, Theodore, and Nicephorus—Presbyters; Basil and Thomas—Deacons; Hierotheus, David, Chariton, Socrates, Comasius, and Eusebius—Monks; and Etymasius, at Tiberiopolis (8th c.).
Luke 13:10-17 (Gospel)
That’s the story of the woman who had a spirit of infirmity for 18 years and I was all set to preach on that.
But our diocesan lectionary had
Luke 18:18-27
That’s the story of the rich young man who asked Our Lord what he must do to inherit eternal life, and it was in our gospel book under the 13th Sunday of Luke.Except that it should have been the 10th Sunday of Luke, or was it?
Anyway, I had to ad lib the sermon on the Epistle and the many martyrs of the day, most of whom were victims of the iconoclasts.
But can anyone explain the discrepancy in the lectionaries?
Khanya 
The lectionary of the Russian Orthodox Church and that of the Church of Constantinople are not identical. The OCA uses the Moscow lectionary, and many of the Mediterranean Churches use the Constantinople lectionary. I’m not sure about other Eastern Orthodox Churches north of Albania, whose lectionary they use or whether they each have their own.
I understand that there exist some liturgical differences between Jerusalem and Constantinople where Moscow keeps Jerusalem practice– I don’t know if the difference comes from this source. If you follow the online lectionary of Greek Orthodox Archdiocese of the United States (goarch.org), that lectionary is the same as that of the Church of Alexandria more than 90% of the time. There are still occasional discrepancies, but sometimes I suspect the discrepancy is due to a printing error in the Nairobi Seminary’s calendar.
I was similarily puzzled a month of two ago. The readings that we’d had at Liturgy were the same as the ones that I had in my lectionary that is published by the fellowship of St John the Baptist in Britain, that seems to cater for both Greeks and Russians. But later that day I came across a homily that Father Gregory Jensen (OCA) had posted on his blog, and it was on a totally different Gospel. I looked up the OCA website and discovered that it was indeed different, whereas the goarch.org site had the same as ours and the Brits. I don’t remember anything like this with Russian parishes in Europe, but I may just not have noticed it. In any case, I was also puzzled, and thought of doing a similar post to this then, but then forgot about it!
I suppose that I should have checked this before, but I’ve just seen that the British lectionary that I mentioned above states: “The cycle of the Sunday Gospels at the Liturgy conforms to the practice of the Ecumenical Patriarchate, which is followed by the Churches of Greece and Cyprus. During the period before the Sunday of the Publican and the Pharisee and after the Exaltation of the Cross, the Russian Church follows a slightly different sequence.”
This is a result of what is colloquially called “the Lukan Jump”: http://orthodoxwiki.org/Lectionary
The Wiki article doesn’t explain why some seem to jump further into Luke than others, so that for some last Sunday was the Tenth Sunday of Luke, while for others it was the Thirteenth.
The previous Sunday was the Entry of the Theotokos into the Temple, and so had a different Gospel reading, and the one before that was the Good Samaritan. So the jump should have been two weeks, but it seems to have been several more.
My understanding is that the difference is not one of degree but of kind—that is, some are doing the jump (mostly the Byzantine churches) and others are not (mostly the Slavic churches).