Q: Concerning the six stages of Israel's relationship as the wife of Jehovah, and the church as the bride of Christ, I am confused if we are talking about one or two “wives” in the Millennium.
A: To answer your question, we are talking about two wives, Israel and the Church, though the metaphor is to be related to two different persons. Israel is related to God the Father, while the Church is related to Christ. This should not be looked upon as purely a bigamist relationship simply because there are three persons in the Godhead: Israel, as the wife of Jehovah, is related to the Father, whereas the Church is related to Christ. Incidentally, it is not unusual for God to picture Himself related to two wives at the same time. You will find Him using the multiple-wife motif for Himself in Ezekiel 23.