You have already established your message issue, such as "greed." And, you have established your counterpoint, such as "generosity." Now is the time to consider them together as in "Greed vs. Generosity."
It is one thing to tell your audience, “Greed leads to self-destruction.” It is another thing to prove it! Using such a premise as the basis for your theme provides you with clear idea of what you hope to say, but it provides precious little guidance in how to say it.
You should focus on the Emotional Argument as the way to prove your point without resorting to cut-and-dried, ham-handed, generalizations and platitudes. Here’s how it works:
“Greed,” in our example premise, does not really stand alone, but has the counter-point of “Generosity.” Although the focus of our story will be on Greed, by also showing the contrasting impact of Generosity, we create a thematic conflict pitting point against counter-point.
In your story you need to explore both point and counterpoint several times to see the relative worth of each. BUT, you should never compare both directly. Rather, the thematic point should be explored on several occasions to see how it fares. Interwoven in other scenes or moments, the counterpoint needs to be separately explored to see how it fares on its own.
As the story progresses, your readers will begin to tally-up the independent value of each, averaging its benefits with its drawbacks. By the end of the story, when all examples of the worth of both point and counter-point have been presented, the audience will arrive at an emotional conclusion that one is better than the other.
For example, Greed may seem to have a greatly negative impact in its first appearance, but slightly positive results in its second. A third appearance might see it as being neutral. Overall, the average of all three appearances rates it as slightly negative.
In contrast, Generosity might also appear greatly negative at first, then highly positive, then slightly positive. In the end, it averages out as slightly positive. The conclusion for the audience is that Greed is somewhat worse than Generosity.
Emotions don’t see things as black and white. By avoiding the simple blanket statement made by a premise and “arguing” the relative worth of point and counter-point over the course of your story, you will create an “emotional argument” which will sway your readers to your point of view, rather than trying to hit them over the head.
In this step, describe how you reveal to your readers the growing thematic conflict in your story through a series of independent illustrations of the benefits and/or detriments of each side of the thematic argument.