Carl F. H. Henry, God, Revelation, and Authority, 6:50-51:

“The Bible at the very beginning emphasizes that God is not merely an acting God of deed-revelation, but a speaking deity also who shapes language as a medium of intelligible communication with man made in his image. Words are the means of transmitting ideas from person to person: it is not centrally in symbols and visions, but especially in words, that the Old Testament focuses its account of divine-human relationships. Moses the lawgiver reports the Word of God; the prophets impart the revealed Word of Yahweh. The Gospels record three occasions on which the invisible God spoke from heaven to acknowledge Jesus as his unique Son: at his baptism (Mark 1:10; cf. Matt. 3:16 f.; Luke 3:21 f; John 1:32 f.); at his transfiguration (Matt. 17:5; cf. Mark 9:7; Luke 9:35; cf. 2 Pet. 1:17); and shortly before the crucifixion (John 12:27–39). Jesus Christ, moreover, commissioned disciples to “preach the word” (Matt. 10:7, 20, 27:20; John 6:63). The secret of Christianity’s expansion was growth of the apostolic word (Acts 6:7, 12:24, 19:20). The orally proclaimed biblical truth, together with the subsequently published Gospel of Christ or teaching of the Bible, was the message of the early Christian church (Rom. 10:17; Gal. 3:2 ff.); the authoritative source of that message was, is and forever remains the transcendent God (1 Thess. 2:2, 13; Gal. 1:11 f.).”