Explain that sin burdens our souls. Then have someone put on the backpack. Place several large rocks in the backpack, talking about the burden of sin, or small sins that one might commit. Have the person in the backpack describe the weight of the backpack. Then say that repentance removes the load, and one by one take the rocks back out and have the person in the backpack describe how he feels to have these burdens lifted. Explain that repentance is like that in our lives.