Certainly God could with His Spirit instruct and justify those whom He would, but it has pleased His wisdom more to instruct and justify those who believe through the foolishness of preaching. The Word is the channel through which the Holy Spirit is given. [There are biblical passages] against those who hold the spoken word in contempt. The lips are the public reservoirs of the church. In them alone is kept the Word of God... Unless the Word is preached publicly, it slips away. The more it is preached, the more firmly it is retained. Reading it is not as profitable as hearing it, for the live voice teaches, exhorts, defends, and resists the spirit of error. Satan does not care a hoot for the written Word of God, but he flees at the speaking of the Word... This penetrates hearts and leads back those who stray.
Martin Luther