The Argument from Miracles
Miracles have traditionally been taken as validations of religious claims. If the Bible is to be believed, then miraculous signs and wonders that testified that it was God working through him accompanied Jesus’ ministry. His resurrection from the dead was the greatest of these miracles, and is still frequently taken today to be a solid reason for believing in the existence of God.
Setting aside the question as to just how strong the evidence for the resurrection, or for any of the other miracles reported in the New Testament, is, religious sceptics frequently cite Hume as having undermined any such argument for belief in the existence of God. Hume noted that there are two factors to assess in deciding whether to believe any given piece of testimony: the reliability of the witness and the probability of that to which they testify.
The testimony of a witness that is both honest and a good judge of that to which they testify is worth much. The testimony of a witness who is either dishonest or not in a position to know that to which they testify is worth little. The reliability of the witness is therefore something that is to be taken into account in deciding whether to believe anything on the basis of testimony.
The probability of that to which they testify, however, is also relevant. If a witness testifies to sighting a flying pig then it is more likely that their testimony is false than that their testimony is true, even if they are a reliable witness.
The reliability required of a witness in order for his testimony to justify belief in that to which he testifies increases as the probability of that to which he testifies decreases. A miracle, however, is by definition an event that is as unlikely as anything else. It will always, therefore, be more likely that the testimony of a witness to a miracle is false than that it is true. So, at least, goes the Humean argument.