A local church is built up by the functioning of all its members with the perfecting of the gifted persons, such as the apostles, prophets, evangelists, and shepherds and teachers (Eph. 4:12), through:
1) the preaching of the gospel to get sinners saved and baptized (Matt. 28:19);
2) the feeding of the new believers in their homes for the growth in life and in truth (John 21:15; 1 Pet. 2:2);
3) the perfecting of the saints in the group meetings for the building up of the Body of Christ (Eph. 4:12); and
4) the prophesying in the church meetings for the building up of the church (1 Cor. 14:1-5, 23-26, 31).
The gifted persons carry out their ministry in perfecting all the members of a local church in a locality, that all the members of that local church will be able to do what the gifted persons can do (Eph. 4:12) in the above-mentioned four items, for the building up of that local church, issuing in the building up of the universal Body of Christ. The gifted persons do not build up the church directly; rather, all the members who have been perfected by the gifted persons build up the church directly.
The building up of a local church is not only for its own building up locally (1 Cor. 14:3), but for the building up of the entire body of Christ universally (Eph. 4:12). Actually, the building up of the local churches is the building up of the Body of Christ, because the local churches are the Body of Christ as its expression. Without the building up of the local churches, by what other way could the Body of Christ be practically built up?