First of all, just what is a miracle? The dictionary defines the term in multiple ways, from “an effect or extraordinary event in the physical world that surpasses all known human or natural powers and is ascribed to a supernatural cause” to “a wonder; marvel”. For the purposes of this blog, it is safe to ignore the second dictionary definition and focus in on some variation of the first. A miracle is the result of an action of God affecting the natural realm. Given that definition, a miracle may not even be noticed by us, especially if it has the appearances of a natural event, like rainfall, or the absence of some event, like an accident that was prevented. Those kinds of miracles are impossible for us to pick out with any certainty, and are generally not identified as miracles by most. More generally we limit miracles to those things for which we have no explanation, apart from God's action, and which are highly uncommon. The signs and wonders performed by Jesus and the apostles in the New Testament are examples of what many will identify as miracles.
So are miracles possible? I believe the answer to this question is largely the same as your answer to the question of God’s existence. If you doubt the existence of God, then it is doubtful you would believe miracles are possible, since there is no God to perform them. On the other hand, if you believe there is a God, who created the universe, then the thought of his interacting with his creation should not be that surprising; although there are some who do accept the existence of a god who created the universe but is not involved with it, and thus do not accept the possibility of miracles.
On the surface then, it would appear that miracles could be used as a proof for the existence of God. And indeed, one of the terms used in the New Testament for miracles is signs. John 20:30-31 in particular demonstrate the use of that term and its purpose.
“Jesus did many other miraculous signs in the presence of his disciples, which are not recorded in this book. But these are written that you may believe that Jesus is the Christ, the Son of God, and that by believing you may have life in his name.”According to John, the purpose for the signs that he recorded was to point a person into a saving relationship with Jesus Christ, the son of God. In fact, I believe that most miracles have a similar purpose; to point people to their creator. I don't see God intervening in the world solely for my physical benefit. God is not like a vending machine where I can drop in a pray and out pops a miracle. Finding a front row parking spot in a crowded lot is not a miracle; it is a fortuitous circumstance.
I cannot recall seeing a miracle similar to what the gospel writers record God doing through Jesus. And so it is tempting to say I have never seen a miracle. But is that really the case? I am instructed to pray to God. A certain portion of that prayer is concerned with thanksgiving and praise. But prayer also includes asking for direction, for provision, for forgiveness. And when I pray, at least when I pray appropriately, I am promised that God will respond. If God responds by helping me to understand his word, by bringing comfort to one in distress, or by healing one that the doctors have given up on; is that not a miracle as well?
Too often today, skeptics respond to talk of miracles in one of two ways. Either they will accept that something unusual has indeed occurred, but it only appears to be a miracle because we have not discovered the scientific explanation for it. Or that the miracle did not actually occur and is a hoax, a misunderstanding, or a coincidence. And they will usually follow that up with a demand to see a miracle performed in a setting where it can be independently verified and validated; similar to the Pharisees of Jesus day (Matthew 12:38). Those men would not have been convinced if Jesus had levitated them 6 feet off the ground and then flew them over the Jordan river and dropped them on the other side. And the skeptics of today would be just as unconvinced.
For those who already believe in God, or who are receptive to that belief; miracles indeed are a sign pointing to God. But to those who have chosen not to believe, no miracle will likely be sufficient to convince them. I am convinced that much of what are called miracles today are not really miracles. But I am also convinced that God will intervene in this world, when appropriate, to point people towards him, and to respond to the prayer of his people.