19 ...baptizing them in the name of the Father and of the Son and of the Holy Spirit,

The Lord knew that despite the gifting of each of the disciples none of them could carry out His commission alone. They needed each other. So, we gave them a vision of churches that He called His body. He will send us the people that will help us carry out the mission. The way we will know the visitor from the member is by the public profession of faith in Christ followed by a demonstration of that decision through baptism.