In the world that God created, the things one does either go His way—i.e., fit into the way He constructed it—or they get him into trouble. The “boomerang” parables (as I like to call them) are an instance of this. For example, speaking of the wicked “schemes’ cooked up by those who “hate knowledge and choose not to fear God,” the writer says, “they will eat the fruit of their way.” He goes on to say, “they will be glutted with their own schemes.” In other words, the evil they plan to do to others, (in one way or another) will providentially find its way back to their own doorsteps (see Proverbs 1:29-31 HCSB).
There is, in this observation, both a warning and a promise. The evil doer can expect, at length, to have to eat the sour fruit that he cultivated to poison the lives of others. He will find that the evil schemes that he has been devising, in time, will pile up in his own house, applicable to no one but himself.
Does this invariably happen? Of course not. God has many ways of dealing with those who seek to do harm to others. But that He often sends the boomerang right back to its source to strike the one who threw it is one of those ways. Ever been smacked in the head with your own weapon? Well, if so, it may be that God was turning your evil into a boomerang.