In Matthew 3:11, John says “I baptize you with water for repentance, but he who is coming after me is mightier than I, whose sandals I am not worthy to carry. He will baptize you with the Holy Spirit and fire.  His winnowing fork is in his hand, and he will clear his threshing floor and gather his wheat into the barn, but the chaff he will burn with unquenchable fire.”
We know that the baptism of Spirit is not water baptism because Jesus did not baptize anyone with water (John 4:2).
Acts 11 provides a clear definition of baptism of the Spirit.
 And he told us how he had seen the angel stand in his house and say, ‘Send to Joppa and bring Simon who is called Peter;  he will declare to you a message by which you will be saved, you and all your household.’  As I began to speak, the Holy Spirit fell on them just as on us at the beginning.  And I remembered the word of the Lord, how he said, ‘John baptized with water, but you will be baptized with the Holy Spirit.’  If then God gave the same gift to them as he gave to us when we believed in the Lord Jesus Christ, who was I that I could stand in God’s way?"  When they heard these things they fell silent. And they glorified God, saying, “Then to the Gentiles also God has granted repentance that leads to life.”
- This message is the Gospel
- They will be saved by believing the message of the Gospel
- Receiving the Spirit upon believing is defined as the Baptism of the Spirit
- They are receiving the lifelong indwelling of the Spirit, the gift promised by Jesus to all who believe.
- Faith and repentance are produced by the Spirit’s work in our hearts.