And when a knight appears on the field full of rhetoric about how he fears encroaching time and wishes to be as bold as possible before then, I go hmm -- yeah, that's central to his motive, but I didn't develop how others react to time. I ought to do that.
Playing with themes can be dangerous, pulling away from the story, but it can also add in orchestrating characters and unifying the story beyond the taking place in the setting.
One weakness of the second two Pirates of the Caribbean flicks was the lack of a theme, especially variations on it. In the first, you had the overarching question of whether a man can be a good man and a pirate. In the next two -- well, you have our official telling the governor that loyalty is no longer the coin of the realm, coin is, but no one else is marked out by old-fashioned loyalty in contrast. Indeed the pirates have to fight because they would tear each other to pieces The only subplots that echoed each other were Davy Jones's tragic romance, and Will and Elizabeth's problems. (I personally think that the reason he asked her to marry him during the battle was that he had seen the two of them tearing each other apart when he was prisoner, and he wants the survivor, if one of them dies, to have the consolation.) But that was just two plot elements in a big scheme.
So, I go to write and ponder as I write what elements are related to time. . . I may even change the emphasis of the religion to dwell on the passage of time and dealing with it.