John 14:15-17a "If you love Me, keep My commandments. And I will pray the Father, and He will give you another Helper, that He may abide with you forever- the Spirit of truth,"…
The Spirit of truth is given only to those who love Him by keeping His commandments.
Acts 1:5, 8 "for John truly baptized with water, but you shall be baptized with the Holy Spirit not many days from now…But you shall receive power when the Holy Spirit has come upon you; and you shall be witnesses to Me in Jerusalem, and in all Judea and Samaria, and to the end of the earth."
Our Lord Jesus told them to wait for the baptism of the Holy Spirit, Who will empower them and they will be His witnesses.
Acts 2:4-6 And they were all filled with the Holy Spirit and began to speak with other tongues, as the Spirit gave them utterance. And there were dwelling in Jerusalem Jews, devout men, from every nation under heaven. And when this sound occurred, the multitude came together, and were confused, because everyone heard them speak in his own language.
At Pentecost when the Holy Spirit came, all the disciples were filled with the Holy Spirit and they spoke in tongues. The devout Jews, who came to Jerusalem to worship and offer sacrifices to Yahweh also had the gift of the interpretation of tongues just like other godly Jews who were filled with the Holy Spirit:- Elizabeth (Luke 1:41-45 Word of wisdom), Zachariah (Luke 1:67-79 Prophecy), Simeon (Luke 2:25-32 Word of knowledge), and in the OT when the Spirit of God was upon Saul and his messengers, all of them also prophesied, etc.
The manifestation of any of the gifts of the Holy Spirit is normally the sign of those 'filled with the holy Spirit'. Speaking in tongues is the most prominent.
Acts 2:14, 36 But Peter, standing up with the eleven, raised his voice and said to them, "Men of Judea and all who dwell in Jerusalem, let this be known to you, and heed my words"...... "Therefore let all the house of Israel know assuredly that God has made this Jesus, whom you crucified, both Lord and Christ."
At Pentecost as promised all the disciples, who had followed and obeyed Jesus, were baptized with the Holy Spirit. The Spirit of truth then leads them into all truth. Peter a fisherman being empowered by the Holy Spirit became His witness, who fearlessly preached the gospel in truth.
Acts 2:37-38 Now when they heard this, they were cut to the heart, and said to Peter and the rest of the apostles, "Men and brethren, what shall we do?" Then Peter said to them, "Repent, and let every one of you be baptized in the name of Jesus Christ for the remission of sins; and you shall receive the gift of the Holy Spirit."
The anointed preaching of Peter convicted the hearers. 'Witnessing in truth fearlessly' is possibly the sign of the baptism in the Holy Spirit and 'speaking in tongue', is possibly a sign of those 'filled with the Holy Spirit', or a gift for service in the church in 1Cor 12:28
Today, with depraved and covetous pastors and televangelists boldly and zealously preaching the prosperity gospel for personal gain, we can discern these wolves with the fruit of the Spirit in Gal 5:22-25