“That the Reformation rightly sought the key mark of the church in the Word of God cannot be doubted on the basis of Scripture. Without the Word of God, after all, there would be no church (Prov. 29:18; Isa. 8:20; Jer. 8:9; Hos. 4:6). Christ gathers his church (Matt. 28:29), which is built on the teaching of the apostles and prophets, by Word and sacrament (Matt. 16:18; Eph. 2:20). By the Word he regenerates it (James 1:18; 1 Peter 1:23), engenders faith (Rom. 10:14; 1 Cor. 4:15), and cleanses and sanctifies [the church] (John 15:3; Eph. 5:26). And those who have thus been regenerated and renewed by the Word of God are called to confess Christ (Matt. 10:32; Rom. 10:9), to hear his voice (John 10:27), to keep his Word (John 8:31, 32; 14:23), to test the spirits (1 John 4:1), and to shun those who do not bring this doctrine (Gal. 1:8; Titus 3:10; 2 John 9). The Word is truly the soul of the church.”
Bavinck, Reformed Dogmatics, 4:312.