Where in the Bible does it tell us to train others? It is implied and taught all over the Scriptures. God trains His people. He even gave us the scriptures to train us in righteousness (2 Timothy 2:16-17). Fathers are to train (Deuteronomy 6). Church leaders are to train.
In order to keep pace with the Lord, we must do more than just train others. While training others, we must train them how to train. This is the only way to keep up with the multiplication of disciples that God wants to bring into being.
One friend was answering the question, "Where does it tell us that everyone needs to be trained to train others?" After referring to a number of key passages such as Ephesians 4:11-13 and 1 Peter 2:9-10, he said a powerful but simple statement. "Matthew 28:19-20 charges all of His people to make disciples of all. If this is the case, then we need to train His disciples to make disciples too."
Note below the way Jesus trained His disciples, and they in turn trained others. This is the sense of 'equipping' in Ephesians 4:11-13. The pastor/teachers are to prepare others to do ministry.