Consider Acts 2:42-43:
They devoted themselves to the apostles’ teaching and to fellowship, to the breaking of bread and to prayer. Everyone was filled with awe at the many wonders and signs performed by the apostles.Here we have a description of what the church is. They devoted themselves to 4 things. The apostles' teaching, fellowship, the breaking of bread and prayer. What is missing? Scripture. Why? Well, the New Testament was not written yet. None of it. In fact, it was likely more than 10 years before any book of the New Testament was written. Yet why was it not written? Mohammed wrote the Koran for his followers. Jesus could have written something for the church. He chose not to do that. He chose to form 12 apostles and start His church on their teaching. The word of God continues to be made flesh and dwells among us.