The Holy Spirit created the Church in its fullness by its descent at Pentecost, not by its later inspiration of writings. Scripture was, evidently, neither immediately necessary nor ultimately sufficient.
The churches had the Old Testament, indeed, the original church in Jerusalem was instituted by Christ during His earthly ministry (only being empowered, not created, by the Holy Spirit at Pentecost) and were not sufficient until they had the full teaching revealed in the New Testament.