They do not mean the same.
1. Your throne, God, is forever. (Here, you are talking to God. Another sentence example is: My car, James, is not for your use.)
2. Your throne is God forever. (Not a good sentence; does not make sense)
3. God is your throne forever. (Simple sentence saying that God is someone's throne. But it does not make much sense, since people don't have thrones.)