Take a big dragnet and hold it while you are discussing the parable. After the word, use the dragnet as you analyze, and have someone help you drag it above there heads. Ask them, if God were to drag His spiritual dragnet across the room, and set down to sort out, by good and bad, would he have to toss them aside? Or would He find them pleasing enough to Him to want to keep them? I found this to be very, very effective in making my young people see the reality of this.