Every believer has been called to preach God's Word, not just pastors of churches. When Christ gave the Great Commission to "preach the gospel to every creature" (Mark 16:15), it was clear that this could be accomplished only if every Christian would actually preach the gospel!
This was practiced first by the members of the church at Jerusalem. Then, when the believers were "all scattered abroad . . . except the apostles" (Acts 8:1), these "laymen" went everywhere preaching the Word. One of the "deacons" selected to relieve the apostles of the "business" affairs of the church was Philip, and he "went down to the city of Samaria, and preached Christ unto them" (Acts 8:5), speaking to great crowds and winning many to Christ. Then shortly afterward, the Lord called him down to Gaza where he met an Ethiopian eunuch, and he "preached unto him Jesus" (Acts 8:35). This teaches plainly that one can preach to a large congregation, but he or she can also preach to one person. It is not the size of the congregation but the theme of the message that makes one a preacher of the Word!
Furthermore, it is not only by word of mouth that Christ is preached; Paul says that "the gospel . . . was preached to every creature [literally, `in every creation'] which is under heaven" (Colossians 1:23). "And how shall they hear without a preacher? . . . But I say, Have they not heard? Yes verily, their sound went into all the earth, and their words unto the ends of the world" (Romans 10:14,18). One can preach verbally to a congregation or to an unseen audience through radio or in writing to a reader, and even a godly lifestyle can "preach" effectively (although not specifically) of the saving work of Christ. Even the heavens declare His glory, and every believer must preach the Word! HMM