Acts 2:37: Now when they heard this, they were pricked in their heart, and said unto Peter and to the rest of the apostles, Men and brethren, what shall we do?

When the Holy Spirit pricks a sinner in the heart, beginning in regeneration and throughout the life of the believer, we cease to hear the words of a man. We hear the words of our Lord himself. That is what happened on the day of Pentecost.

An earthen vessel was speaking, but whose word was being preached? It was a sinner preaching but whose Spirit sent forth the Word? When the folks at Pentecost were made to hear, who did they hear? Acts 2: 33: Therefore [the Lord Jesus Christ] being by the right hand of God exalted, and having received of the Father the promise of the Holy Ghost, he hath shed forth this, which ye now see and hear.

Some only heard the voice of a men speaking in unlearned languages. Some were listening to hear if Peter would tell them what man must do or must not do according to man's own ability. They were not listening to hear the Word of the One whom they had just rejected. But the Spirit made some to truly hear and it had a sure and certain effect. Act 2:37: Now when they heard [their Lord speak through the Holy Spirit], they were pricked in their heart and said unto Peter and to the rest of the apostles, Men and brethren, what shall we do?