There will always be a need for the Word of God to be shared with others. It needs to be taught to the lost as well as Christians who have already obeyed the gospel. After the first Christians obeyed the gospel in Acts 2, we see they continued to listen to the apostles teaching. With the later epistles from Paul and Peter, we see that the church continued to receive teaching. Paul even wrote "minister letters" to Timothy and Titus, who were working for the Lord as preachers.