Here are some notes from Augustine’s Harmony of the Evangelists 1.35, which I shared on twitter (@Riddle1689). As he concluded Book 1, Augustine returned to his purpose for this book, namely, to defend the unity and harmony of the Four Gospels against the pagan critics. One of their arguments was that Jesus left behind no writings and that his disciples had distorted the account of his life and teachings.
Why does Augustine say the four Gospels have essential unity and can be harmonized?
Harmony 1.35: It is because Christ "stands to all his disciples in the relation of the Head to the members of his body."
Harmony 1.35: "Therefore when those disciples [the evangelists] have written matters which he declared and spake to them, it ought not by any means to be said he [Jesus] has written nothing of himself; since the truth is, that his members have accomplished only what they became acquainted with by the repeated statements of the Head."
Harmony 1.35: "For all that he [Jesus] was minded to give... he commanded to be written by those disciples whom he used as if they were his own hands."
Harmony 1.35: When one reads any of the four Gospels "he might look upon the actual hand of the Lord himself... to see it engaged in the act of writing."