I hope this is an ok place voice this idea. I don't know what theme is next but if it's Christ related, is it possible that relating old testament promises and beautiful things spoken over Israel or prophesied about the benefits of the messiah could be something that portrays Christ in ways we might miss in the new testament? Like for example, many times in the old testament, God speaks His heart over His people. Paul says we are grafted in to the promise and inheritance which means those things that reveal God's heart in the old testament over Israel is also for the believer in Christ. Something like that.
So merging the two somehow would be cool in a Christ themed set.
So a card about the old testament promises gets played or activated when a character with the holy spirit enters the scene or something like that.