As the Quran was revealed, the Prophet and the believers following him recited the text by heart and it was also written down by the scribes in his following.
It therefore starts off with two elements of authenticity that the Gospels do not possess. This continued up to the Prophet's death.
At a time when not everybody could write, but everyone was able to recite, recitation afforded a considerable advantage because of the double-checking possible when the definitive text was compiled.