17 The multitude of the hearers was confounded—it was a second confusion, in the room of that first evil one at Babylon. For in that confusion of tongues there was division of purpose, because their thought was at enmity with God; but here minds were restored and united, because the object of interest was godly. The means of falling were the means of recovery. Wherefore they marvelled, saying, How hear we them speaking? No marvel if you be ignorant; for even Nicodemus was ignorant of the coming of the Spirit, and to him it was said, The Spirit breathes where it lists, and you hear the voice thereof, but canst not tell whence it comes, and whither it goes; but if, even though I hear His voice, I know not whence he comes, how can I explain, what He is Himself in substance?
Source: Catechetical Lectures (New Advent)