This verse is interpreted in one of two ways. The traditional 3-step interpretation is, "Until you speak in tongues, you really aren't a Christian." The other interpretation is, "You cannot confess or declare Christ's Lordship over your life except by the Holy Spirit."
This is important because if the first interpretation is right, then speaking in tongues is essential for salvation. If the second is correct, then salvation occurs at faith rather than speaking in tongues. I had always heard the first interpretation and believed it for many years. I now see the second interpretation as the valid one. When you believe the Holy Spirit comes to dwell in you.
I John 4:13, 15: "We know that we live in Him and He in us, because He has given us of His Spirit...If anyone acknowledges that Jesus is the Son of God, God lives in him and he in God."
The baptism in the Holy Spirit is a separate event from salvation, although it can happen at the same time.
When we see the believers in
Acts 8 and
Acts 19 filled with the Holy Spirit, we see that they were already believers before they received the HS. There was great joy in Samaria before they were baptized in the Holy Spirit. Now why would they be rejoicing if they were still yet not born again? Why would there be cause to rejoice if they weren't saved and had the Spirit of God dwelling in them?
Jesus said the baptism of the HS would empower the disciples to be witnesses. Paul said the Gospel of Jesus Christ is the "power of God". Jesus said that the HS would testify of Him. The purpose of the baptism of the HS is to empower the believer, already saved and a disciple of Jesus, to be the witness He has called them to be.