Your speech could discuss examples that you brainstorm that illustrate the truth of the statement. You would need to think of times when good deeds came back to the doer of the good deed, or when bad things happened to bad people. For example, the Extreme Makeover Home edition program frequently features people who are doing something extraordinary in their community, but who living in a terrible house. The television crew and construction group "reward" the way they live their lives with a new home. The intention shows that what goes around (good deeds for others) comes around (a good deed done for you.) The opposite is true with criminals. A gang members harms a rival gang member, and then is killed in a retaliation drive-by shooting. What goes around (violence) comes around (more violence). You need to think of other examples where this principle is true.