27 If now the question is asked, as to which of the words we are to suppose the most likely to have been the precise words used by John the Baptist, whether those recorded as spoken by him in Matthew's Gospel, or those in Luke's, or those which Mark has introduced, among the few sentences which he mentions to have been uttered by him, while he omits notice of all the rest, it will not be deemed worth while creating any difficulty for oneself in a matter of that kind, by any one who wisely understands that the real requisite in order to get at the knowledge of the truth is just to make sure of the things really meant, whatever may be the precise words in which they happen to be expressed.
For although one writer may retain a certain order in the words, and another present a different one, there is surely no real contradiction in that. Nor, again, need there be any antagonism between the two, although one may state what another omits. For it is evident that the evangelists have set forth these matters just in accordance with the recollection each retained of them, and just according as their several predilections prompted them to employ greater brevity or richer detail on certain points, while giving, nevertheless, the same account of the subjects themselves.
Source: The Harmony of the Gospels (New Advent)