Ask two people to come to the front. For this example, let's call them John and Mary.
Tell the congregation that John is a faithful witness and wins people to the Lord regularly. Send him out to get one person from the congregation and bring him to the front with him, representing his new convert.
Tell the congregation that Mary is also a faithful witness, and send her out to get one more person. But add that Mary also trains her disciples to do exactly what she does.
Now sent John out to get one more person and bring him to the front. There are now 3 at the front on John's side.
It's Mary's turn to go, but since she has trained her disciple to be a witness, both of them go to get one more person each. There now 4 at the front on Mary's side.
Remind the congregation that John is a faithful witness, but he doesn't train them to go and do the same. But Mary trains her disciples to witness, but also to train others as faithful disciples. She passes the task of the Great Commission down through her spiritual children and grandchildren.
Repeat this process again. John brings one more person to the front (4 total), but each person from Mary's side goes out and brings one more person (8 total).
If there are enough people in the congregation, repeat the process yet again. John will have 5 on his side, and Mary will have 16. At this point, people get the full impact of multiplication as opposed to mere addition.
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