Matthew 28:19-20 Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost: (20) Teaching them to observe all things whatsoever I have commanded you: and, lo, I am with you alway, even unto the end of the world. Amen.
After we go, teach, and Baptize, we must teach new Christians what we know. Once a new christian joins the church or accepts Jesus gift of salvation it is then up to the others in the church to guide them. The Sunday school teacher shares the lesson in the Sunday school books. There are those that work with the children of the church. There are many who teach new Christians. Then there is the preacher. His jobs is to instruct us on how to teach the new Christians. We are all responsible for teaching new converts.
The song "Rescue The Perishing" sums up the message of the Great Commission.