Eusebius wrote, “It is my purpose to write an account of the successions of the holy apostles, as well as of the times which have elapsed from the days of our Saviour to our own; and to relate the many important events which are said to have occurred in the history of the
Church; and to mention those who have governed and presided over the
Church in the most prominent
parishes, and
those who in each generation have proclaimed the divine word either orally or in writing.” Eusebius of Cæsarea Church History, I.1., (260-341). Why didn’t the good Bishop of Cæsarea write a History of the “Churches” (plural), or the elect, or the congregational, or the Baptist? Its clear Eusebius is discussing an emerging community of faith (called Catholic today), not a single congregation. Also, note that the Church taught “orally,” that’s to say, God is free to reveal himself outside the confines of the Bible; for that matter, outside the confines of Paul’s epistles.
JoeT