I don’t think it coincidence that “a sound like the blowing of a violent wind” was the very first sign of the Holy Spirit at Pentecost. The thing about wind is that you can’t see it, yet no one ever questions it’s existence or it’s effectiveness. We know it is present not by seeing it but by how it moves and bends the objects around us. This is the same with the Holy Spirit. We can’t see Him but we can see the evidence of His presence; the bending and breaking of stiff-necked men.