First, grace changes the lives of people who have been chosen and prepared for it:
And suddenly there came a sound from heaven, as of a mighty wind coming, and it filled the whole house where they were sitting. And there appeared to them parted tongues as it were of fire, and it sat upon every one of them: and they were all filled with the Holy Ghost.
Next, their behavior and capabilities change:
And they began to speak with divers tongues, according as the Holy Ghost gave them to speak.
Next, the people around them notice something different:
And when this was noised abroad, the multitude came together, and were confounded in mind, because that every man heard them speak in his own tongue. And they were all amazed, and wondered, saying: Behold, are not all these, that speak, Galileans? And how have we heard, every man our own tongue wherein we were born?
Everyone wonders at the change, but some people mock and deride:
And they were all astonished, and wondered, saying one to another: What meaneth this? But others mocking, said: These men are full of new wine.
Those who know explain to the ones who wonder:
But Peter standing up with the eleven, lifted up his voice, and spoke to them: Ye men of Judea, and all you that dwell in Jerusalem, be this known to you, and with your ears receive my words. For these are not drunk, as you suppose, seeing it is but the third hour of the day. But this is that which was spoken of by the prophet Joel: And it shall come to pass, in the last days, (saith the Lord,) I will pour out of my Spirit upon all flesh: and your sons and your daughters shall prophesy, and your young men shall see visions, and your old men shall dream dreams.
And they convey the guilt of the hearers – a call to repentance:
Ye men of Israel, hear these words: Jesus of Nazareth, a man approved of God among you, by miracles, and wonders, and signs, which God did by him, in the midst of you, as you also know: This same being delivered up, by the determinate counsel and foreknowledge of God, you by the hands of wicked men have crucified and slain.
The hearers feel the prick of conscience, and acknowledge the need to change their beliefs and their behavior:
Now when they had heard these things, they had compunction in their heart, and said to Peter, and to the rest of the apostles: What shall we do, men and brethren?
Those who know call the hearers to join themselves to Christ, and separate themselves from the world:
But Peter said to them: Do penance, and be baptized every one of you in the name of Jesus Christ, for the remission of your sins: and you shall receive the gift of the Holy Ghost. For the promise is to you, and to your children, and to all that are far off, whomsoever the Lord our God shall call. And with very many other words did he testify and exhort them, saying: Save yourselves from this perverse generation.
And the hearers do so:
They therefore that received his word, were baptized; and there were added in that day about three thousand souls. And they were persevering in the doctrine of the apostles, and in the communication of the breaking of bread, and in prayers.
Such is the pattern of all conversion. To this very day, and until the end of the world, those outside of our Lord will experience a moment of clarity. They will pursue this insight until they encounter the truth, and the truth will change their hearts and their lives, and they will never be the same again.
