th this,

"He Who was manifest to men has given us the Gospel under four
aspects, but bound together by one Spirit."

Then he refers to the four living creatures of the vision in the
Revelation, and proceeds,--

"And, therefore, the Gospels are in accord with these things, among
which Christ is seated. For that according to John relates His
original effectual and glorious generation from the Father, thus
declaring, 'In the beginning was the word,' &c.... But that
according to Luke, taking up His priestly character, commences with
Zacharias the priest offering sacrifice to God. For now was made
ready the fatted calf, about to be immolated for the finding again
of the younger son. Matthew again relates His generation as a man,
saying, 'The Book of the generation of Jesus Christ, the Son of
David, the Son of Abraham;' and also, 'The birth of Jesus Christ was
on this wise.' This, then, is the Gospel of His humanity, for which
reason it is, too, that the character of an humble and meek man is
kept up through the whole Gospel. Mark, on the other hand, commences
with a reference to the prophetical spirit coming down from on high
to men, saying, 'The beginning of the Gospel of Jesus Christ, as it
is written in Esaias the prophet,' pointing to the winged aspect of
the Gospel: and on this account he made a compendious and cursory
narrative, for such is the prophetical character." (Iren., Bk. iii.
ch. xi.)

Clement of Alexandria, speaking of a saying ascribed to our Lord,
writes:--

"In the first place, then, in the four Gospels handed down amongst
us, we have not this saying; but in that which is according to the
Egyptians." (Miscellanies, iii. ch. xiii.)

Tertullian writes thus:--

"Of the Apostles, therefore, John and Matthew first instil faith
into us; whilst, of Apostolic men, Luke and Mark renew it
afterwards. These all start with the same principles of the faith,
so far as relates to the one only God the Creator, and His Christ,
how that He was born of the Virgin, and came to fulfil the law and
the prophets. Never mind if there does occur some variation in the
order of their narratives, provided that there be agreement in the
essential matter of the faith in which there is disagreement with
Marcion." (Tertullian against Marcion, iv. c. ii.)

Such are the explicit declarations of these