The Catholic Church kept the teachings alive in Latin, pictures and statues until they canonized the Bible [for the Johnny-come-latelys who think Protestants created it].
Actually, the only complete pre-vulgate manuscripts we all have indicate that the Church did write everything down in the Greek, many dfferent times and in many different places. So preservation isn’t really an issue anymore, unless you are looking at the gulf between Constantine in the 300s and between Christ around 35 or so.
That is the only gap and a gap only of complete original manuscripts. And they all, up until this gap say the same thing that the Chruch wrote down the teachings of Christ in the language used at the time, to great cost and effort preserved them.