“And they were all filled with the Holy Spirit and began to speak in other tongues as the Spirit gave them utterance.” (Acts 2:4)
When the Holy Spirit was poured out on the feast of Pentecost, this was visible through various signs: there was a sound like a mighty wind, divided tongues as of fire rested on the heads of the apostles, and they began to speak in other languages.
People from many different countries, who were in Jerusalem for the feast, were astonished: “Are not all these who are speaking Galileans? And how is it that we hear, each of us in his own native language?” (Acts 2:7-8).
These signs were visible and audible for everyone, and people were amazed. But the miracle that happened within people’s hearts was still greater: the apostles spoke the Word of God with boldness, and over 3000 people were saved (Acts 2:41, see also 4:33). That is exactly what Jesus had promised: the Holy Spirit convicted people of sin and righteousness and judgment. And this work of the Spirit was not temporary like the sound of the wind and the tongues as of fire. The Lord added to the group of believers day by day, and the apostles kept preaching the Gospel with boldness (see e.g. Acts 2:47 and 4:31).
Do you realize that boldness in preaching and repentance are fruits of the Holy Spirit just as much as speaking in other languages?