The promise was that God would make Zerubbabel a signet, meaning God would honor him in some way, possibly putting him in charge of something, when the Messiah comes to rule the world.  Honestly, the meaning of God making him a signet seems unclear to me, so that was the best explanation I could give.  All I know is that whatever God plans to do for the guy is going to be pretty cool.

Oh, yeah!  Who is the Messiah?

-Moses-

-David-

-John the Baptist-

-Jesus-