6 Why, then, should the narrative of the birth not be the gospel, since it conveys such good news as heals our malady? Is it because Matthew begins, not like Mark, with the words, "The beginning of the gospel of Jesus Christ," but, "The book of the generation of Jesus Christ?" In this way, John, too, might be said not to have written the gospel, for he has not the words, Beginning of the gospel, or Book of the gospel, but, "In the beginning was the Word." Perhaps the clever word-maker Faustus will call the introduction in John a Verbidium, as he called that in Matthew a Genesidium.
The wonder is, that you are so impudent as to give the name of gospel to your silly stories. What good news is there in telling us that, in the conflict against some strange hostile nation, God could protect His own kingdom only by sending part of His own nature into the greedy jaws of the former, and to be so defiled, that after all those toils and tortures it cannot all be purged? Is this bad news the gospel? Every one who has even a slender knowledge of Greek knows that gospel means good news.
But where is your good news, when your God himself is said to weep as under eclipse till the darkness and defilement are removed from his members? And when he ceases to weep, it seems he becomes cruel. For what has that part of him which is to be involved in the mass done to deserve this condemnation? This part must go on weeping for ever. But no; whoever examines this news will not weep because it is bad, but will laugh because it is not true.
Source: Reply to Faustus the Manichaean (New Advent)