When the Day of Pentecost had fully come, they were all with one accord in one place. And suddenly there came a sound from heaven, as of a rushing mighty wind, and it filled the whole house where they were sitting. Then there appeared to them divided tongues, as of fire, and one sat upon each of them. And they were all filled with the Holy Spirit and began to speak with other tongues, as the Spirit gave them utterance.
They were told to return to Jerusalem and await a visit from the Holy Spirit. That was all they were told. We know from subsequent verses that they met together and began to pray, but the road ahead would be a mystery. The coming of the Holy Spirit was some nebulous idea, but there was nothing concrete about this visitation. No one could have known what to expect. What they experienced was an event that no one could have explained any other way. They would find themselves speaking in tongues they did not know. Other people who spoke those tongues witnessed this display. They had not known how the Spirit would appear to them, but it was clear when He entered the room.
A friend of mine was involved in a pretty bad accident in which her vehicle flipped over more than once. She called me from the scene and was in hysterics, but she was not hurt. If anything, she was confused. She described the condition the car was in and that the windows were all broken, but she could not explain how she had exited the car without a scratch. There was glass everywhere except on her. Even the emergency personnel who responded could not believe that she was not harmed. When asked, she kept repeating that God had pulled her out of the car. She knew that the hand of God had saved her from that wreck, and I can say that I knew it as well.
Some people say that supposedly miraculous events are attributed to God simply because those who experience them cannot think of another explanation. I say that those who know God will recognize his miracles as He performs them. They should be able to discern his presence and his movement. They should know his character well enough that, even when He moves in a way they do not expect, they can recognize it as still being him. Sometimes you just know, and we should be close enough to God for that to be enough of an explanation. Father, make us sensitive to your movement so that we would have confidence in knowing when You have worked a miracle for us.