The Christian can respond to this argument in a few ways
On a first note we can entirely reject this criteria. A skeptic, specifically a philosophical naturalist, will define a miracle as an extraordinary claim. The naturalist’s hope then is that all miracle claims can be denied on this basis because, he will argue, no evidence ever presented can be “extraordinary” enough. Theists, or anyone else for that matter, needn’t accept this criteria defined by the naturalist. Not only do theists not share the constraints of philosophical naturalism, but the naturalist needs to do far more than dismiss evidence out of hand if he wants to be taken seriously. Rather, he needs to provide compelling evidence in support of his view, as well as provide an answer to the alleged evidence presented by theists. To be fair, many naturalists do attempt to do this, and theists need to be able to respond accordingly. Sadly, however, within atheist circles there is a louder bunch who’d rather simply dismiss evidence wholesale rather than consider it. Theists needn’t take the latter seriously like he ought to the former.
Secondly, though it might seem logical at first, extraordinary claims do not require extraordinary evidence, rather they require sufficient evidence. An extraordinary claim may very well be the best explanation for a set of data and if so it would be silly to deny it based on an unwarranted criteria. If we were to apply this standard to daily life then we might just as well reject other improbable (“extraordinary”) events such as the fact that somebody can actually win the lottery, or get lucky at the casino.
Moreover, probability is an important consideration. Now, given that Jesus’ resurrection is a miracle, this argument is often made against it. Essentially the skeptic would argue that the historical evidence for the resurrection is not “extraordinary” enough to grant the conclusion that there was in fact a supernatural miracle of God intervening in space-time to resurrect Jesus. After all, a resurrection should be considered an extraordinary claim because we don’t often see people being raised from the dead (on this note I like to link atheists to the testimony of a professor and anthropologist, an atheist himself, who did actually witness somebody getting up from the dead). But there is a response to this.
Firstly, that Jesus resurrection was an improbable event, given that physical resurrections from the dead probably don’t occur much, is exactly what we would expect should God desire to grab our attention. This is one of the central features of the gospel message for Christians, namely that God sacrificed Jesus, himself, on a cross for the atonement of humankind’s sin. This would have been an ineffective and dumb act on God’s part if bodily resurrections were a common occurrence. If it were it wouldn’t be considered a miracle or anything worth getting excited about. It is precisely because of its improbability that Christians can boast God’s action in history.
Secondly, apologists routinely point out that Jesus’ resurrection is best explained by a set of facts known as the minimal facts. The minimal facts approach only considers historical data that the majority of scholars accept. We know of these facts largely thanks to the efforts of philosopher and historian Garry Habermas who analyzed a few thousand academic articles penned by numerous experts in historical fields on the subject of the historical Jesus. Habermas identified four facts that are used by Christians to argue for the historical resurrection of Jesus; these are that -1- Jesus died via crucifixion, -2- that he was buried, -3- that three days later the tomb Jesus was placed in was found empty, and -4- that the disciples, the persecutor Paul, the doubting brother James, and others had post-mortem experiences of the resurrected Jesus that convinced them that he was raised from the dead.
This is where we can turn the naturalist’s argument on its head. If we were to apply probability to these four basic facts we would need to then ask “What would the probability be of the resurrection not happening in hindsight of these four facts?” To which philosopher William Craig answers: “It is highly, highly, highly, improbable that we should have that evidence [four facts] if the resurrection had not occurred” (1).
In other words, it is precisely because we have these historical facts that makes Jesus’ resurrection far more probable than not.
1. Craig, W. 2012. Stephen Law on the Non-existence of Jesus of Nazareth. Available.