After Jesus’ resurrection from the dead, (before He ascended into heaven), He exclaimed, "But you shall receive power when the Holy Spirit has come upon you; and you shall be my witnesses in Jerusalem and all Judea and Samaria and to the end of the earth” (Acts 1:8). 

"He who believes and is baptized will be saved; but he who does not believe will be condemned. And these signs will follow those who believe: In My name they will cast out demons; they will speak with new tongues; they will take up serpents; and if they drink anything deadly, it will by no means hurt them; they will lay hands on the sick, and they will recover.” (Mk.16:16–18) 

To be an effective Christian witness without the authentic “Baptism of the Holy Spirit” with proof of the “signs” following, is next to impossible (Mk.16:16–18).

There has been a serious “spiritual crime” perpetrated upon Christian believers whom are told that they received the Holy Spirit when they had not. Many have believed they have received when they where baptized in water. The experience of forgiveness when being born again of water, is a wonderful cleansing experience (Jn. 3:5), and often mistaken for the Baptism of the Holy Spirit.

"Jesus answered, “Most assuredly, I say to you, unless one is born of water and the Spirit, he cannot enter the kingdom of God. (Jn. 3:5)

"I (John) baptize you with water for repentance. But after me comes one who is more powerful than I, whose sandals I am not worthy to carry. He (Jesus) will baptize you with the Holy Spirit and fire." (Matt. 3:11)

There is only one time in the Book of Acts where the Water Baptism and the Baptism of the Holy Spirit were combined. It was in the home of Cornelius:  

"While Peter was still speaking these words, the Holy Spirit fell upon all those who were listening to the message. All the circumcised believers who came with Peter were amazed, because the gift of the Holy Spirit had been poured out on the Gentiles also. For they were hearing them speaking with tongues and exalting God. Then Peter answered, 'Surely no one can refuse the water for these to be baptized who have received the Holy Spirit just as we did, can he?' And he ordered them to be baptized in the name of Jesus Christ. Then they asked him to stay on for a few days." (Acts 10:44–48)

All other times throughout the bible, the Baptism of the Holy Spirit was received as a second experience to Salvation. Today many Christians believe that they had received when they first believed, when they had not. When looking into the scriptures, we find at least four instances of being born again of the Spirit as a separate experience to Salvation (Jn. 3:5):

1) the one hundred and twenty in the Upper Room,

"When the Day of Pentecost had fully come, they were all with one accord in one place. And suddenly there came a sound from heaven, as of a rushing mighty wind, and it filled the whole house where they were sitting. 3 Then there appeared to them divided tongues, as of fire, and one sat upon each of them. And they were all filled with the Holy Spirit and began to speak with other tongues, as the Spirit gave them utterance. (Acts 2:1-4);

2) in Philips ministry (Acts 8:4–8;14–17),

"Now when the apostles who were at Jerusalem heard that Samaria had received the word of God, they sent Peter and John to them, who, when they had come down, prayed for them that they might receive the Holy Spirit. For as yet He had fallen upon none of them. They had only been baptized in the name of the Lord Jesus. Then they laid hands on them, and they received the Holy Spirit. (Acts 8:14–17);

3) when Saul became Paul (Acts 9:1–17),

"And Ananias went his way and entered the house; and laying his hands on him he said, “Brother Saul, the Lord Jesus, who appeared to you on the road as you came, has sent me that you may receive your sight and be filled with the Holy Spirit.” (Acts 9:17);

4) and with John the Baptist’s disciples (Acts 19:1–7),

"Then Paul said, “John indeed baptized with a baptism of repentance, saying to the people that they should believe on Him who would come after him, that is, on Christ Jesus.” When they heard this, they were baptized in the name of the Lord Jesus. And when Paul had laid hands on them, the Holy Spirit came upon them, and they spoke with tongues and prophesied.7 Now the men were about twelve in all. (Acts 19:4-7).

Many believers have been taught that they have received Holy Spirit at the same time as their Salvation, and that the “Baptism with the power of the Holy Spirit” will follow. Many of these same Christians have told me that they “feel something is missing in them” or “feel empty” (Gal. 5:22-23). They are correct since ”the Holy Spirit had not fallen upon them yet in any sense.”

The Baptism of the Holy Spirit is an important part of God's Salvation package. In most cases, it is a second experience received by ”prayer and the laying on of hands” by another spirit-filled believer, as Peter and John did with the new believers in the Book of Acts.

"When they arrived, they prayed for the new believers there that they might receive the Holy Spirit, because the Holy Spirit had not yet come on any of them; they had simply been baptized in the name of the Lord Jesus. Then Peter and John placed their hands on them, and they received the Holy Spirit. (Acts 8:15–17)

Jesus explained, “For he whom God has sent utters the words of God, for it is not by measure that he gives the Spirit” (Jn. 3:34). Which means that unlike Elisha who received a double portion of the Spirit when he was taken up (2 Kings 2:9–12), Christian believers when Baptized in the Holy Spirit, receive the FULL power of the Holy Spirit to be effective witnesses.

Therefore Christians without the Holy Spirit and the signs following as in Mk. 16:17-20, who feel powerless and empty and had the experience of forgiveness and cleansing of sin, can receive the Baptism of the Holy Spirit by the laying on of hands. If believers do not have the “signs of authenticity” as in Mark 16:17-20, then they have not received the Holy Spirit.

"And these signs will accompany those who believe: In my name they will drive out demons; they will speak in new tongues; they will pick up snakes with their hands; and when they drink deadly poison, it will not hurt them at all; they will place their hands on sick people, and they will get well.” After the Lord Jesus had spoken to them, he was taken up into heaven and he sat at the right hand of God. Then the disciples went out and preached everywhere, and the Lord worked with them and confirmed his word by the signs that accompanied it." (Mk. 16:17–20).

Furthermore, Paul tells us that there are three groups of people in the church: first, unbelievers; secondly, believers who have received the Gift of the Holy Spirit; and thirdly, a group who have refused to receive the Baptism and the Gifts of the Holy Spirit (Rom. 12:6–8; 1 Cor. 12:8–10). Those who refuse are neither unbelievers nor full-fledged Christians; they are referred to as “outsiders, ungifted or laymen” (translated from greek, idiotia).

"Therefore tongues are for a sign, not to those who believe but to unbelievers; but prophesying is not for unbelievers but for those who believe. Therefore if the whole church comes together in one place, and all speak with tongues, and there come in those who are uninformed or unbelievers, will they not say that you are out of your mind? But if all prophesy, and an unbeliever or an uninformed person comes in, he is convinced by all, he is convicted by all.  And thus the secrets of his heart are revealed; and so, falling down on his face, he will worship God and report that God is truly among you. (1 Cor.14:22–25)

The power of the Holy Spirit guarantees our salvation, and is an essential part of the Salvation package and for ministry.

"In Him you also trusted, after you heard the word of truth, the gospel of your salvation; in whom also, having believed, you were sealed with the Holy Spirit of promise, who is the guarantee of our inheritance until the redemption of the purchased possession, to the praise of His glory." (Eph. 1:13–14)