First thing i wan to say is that you shouldn’t watch Faith for: Logic, narrative flow, or a satisfying overarching story line.
It’s possible to enjoy this show for its slow-boil romance, but the second you give your brain cells free reign everything falls to pieces.
I mean it's like those light novels you read that you know has some messages but is not a brain twister and i'm pretty sure that's what they were aiming for.

If you want to watch a historical, fantasy romantic drama with LEE-MIN HO as the main lead(That's why i watched it).
Go for it. And this drama is really good, You will love it. Not the best drama by Lee-Min Ho but, neither the worst too.
I loved it, and i like the ending too. It's a decent heartwarming above average romantic historical drama