But he never once intimates the least suspicion of such a thing--never questions the Gospels as books of history--nor denies the miracles recorded in them, but attributes them to magic.[70] Here, then, we have testimony as acceptable to an Infidel as that of Strauss or Voltaire--in fact, utterly undeniable by any man of common sense--that the New Testament was well known and generally received by Christians as authoritative, when Celsus wrote his reply to it, in the end of the second century.

If it was a forgery, it was undoubtedly a forgery of old standing, if he could not detect it.
But we will go back a step farther, and prove the antiquity of the New Testament by the testimony of another enemy, two generations older than Celsus.

The celebrated heretic, Marcion, lived in the beginning of the second century, when he had the best opportunity of discovering a forgery in the writings of the New Testament, if any such existed; he was excommunicated by the Church, and being greatly enraged thereat, had every disposition to say the worst he could about it.

He traveled all the way from Sinope on the Black Sea, to Rome, and through Galatia, Bithynia, Asia Minor, Greece, and Italy, the countries where the apostles preached, and the churches to which they wrote, but never found any one to suggest the idea of a forgery to him.

He affirmed that the Gospel of Matthew, the Epistle to the Hebrews, those of James and Peter, and the whole of the Old Testament, were books only for Jews, and published a new and altered edition of the Gospel of Luke, and ten Epistles of Paul, for the use of his sect.[71] We have thus the most undoubted evidence, even the testimony of an enemy, that these books were in existence, and generally received as apostolical and authoritative by Christians, at the beginning of the second century, or within twenty years of the last of the apostles, and by the churches to which they had preached and written.
The only remaining conceivable cavil against the genuineness of the books of the New Testament is: "That they bear internal evidence of being collections of fragments written by different persons--and are probably merely traditions committed to writing by various unknown writers, and afterward collected and issued to the churches under the names of the apostles, for the sake of greater authority." This theory being received as gospel by several learned men, has furnished matter for lengthy discussions as to the sources of the four Gospels.
Translated into English, it amounts to this, that Brown, Smith, and Jones wrote out a number of essays and anecdotes, and persuaded the churches of Ephesus, Jerusalem, Antioch, Corinth, and the rest, to receive them as the writings of their ministers, who had lived for years, or were then living, among them; and on the strength of that notion of their being the writings of the apostles, to govern their whole lives by these essays, and lay down their lives and peril their souls' salvation on the truth of these anecdotes.