Comparing Sophocles with Homer (Essay Help)

I have to write an essay, but I just need help with coming up with some ideas.

In the essay, I have to compare/contrast the plays "Ajax" OR "Electra" (both are by Sophocles) with the "Iliad" (by Homer). You CANNOT mention similarities/differences in plot between the two, but rather why each author wrote the play (what message were both trying to relay?).

Thanks again. Help would be much appreciated!