A "revolution" can mean a complete change in the government of a nation or an institution. A "counterrevolution" refers to a change back. A counterrevolution un-does the revolution and restores the previous form of government. The Church of England is a large organization with a complex power structure. Most large organizations contain within them "factions," groups struggling for control of the organization. Two such groups within the Church of England are the High Church and Low Church factions. The theological difference is that the High Church faction wants the Church of England to be more like Catholicism, the Low Church faction wants it to be more like Protestantism. I don't know enough about the history of the Church of England to say much. With regard to what the language means, the sentence is saying that a big national meeting "constituted a virtual High Church counterrevolution." This means that sometime before, there must have been a "revolution." Probably the Low Church faction had gained power, and made some changes so big they were "revolutionary." But in this Convocation the High Church faction got the upper hand and took back power. I don't know the history--but these things ARE usually financial. They were probably fighting about money. But that's just my guess.