Acts 1:8 But ye shall receive power, after that the Holy Ghost is come upon you: and ye shall be witnesses unto me both in Jerusalem, and in all Judaea, and in Samaria, and unto the uttermost part of the earth.
Jesus told His disciples before He left to tarry in Jerusalem until they received power from on high Luke 24:49. He was talking about receiving the Holy Ghost in the experience of being filled with the Holy Ghost and speaking in other tongues or languages Acts 2:1-4. This experience is subsequent to salvation and is for all Believers to experience. We can be full of the Spirit by being full of the Word (John 6:63) and full of prayer (Acts 4:31), but that is not the same as being baptized with the Holy Ghost. When we get baptized in the Holy Ghost, we speak in tongues. The Bible evidence (five recorded instances) seems overwhelmingly clear that when one is initially baptized with the Holy Ghost they speak in tongues. Look at Acts 2:4; 8:14-19; 9:17; 10:44-46; 19:6, and you see that in three of the five instances, it is plainly stated they spoke in tongues (Acts 2,10,19). In the other two instances (Acts 8, 9) it is strongly implied.
It is significant to understand that Jesus made the focus of this experience on receiving the Holy Ghost and power not merely the supernatural speaking in other tongues. The initial outpouring of the Holy Ghost in Acts 2 also adds insight as to the purpose of this experience of power. It happened because the disciples were in Jerusalem, not just because Jesus told them to tarry there, but because of the feast of Pentecost. Three major feasts where every male had to appear in Jerusalem were Passover, Pentecost, and Tabernacles. Pentecost was fifty days after Passover. If they understood Jesus as the final Passover Lamb and fulfillment of that feast, then Pentecost was next, and the coming of the Holy Ghost was a part of the fulfillment of that feast.
Do you know that the feast of Pentecost is also called the feast of Harvest? Exodus 23:16 says, “And the feast of harvest, the firstfruits of thy labours, which thou hast sown in the field: and the feast of ingathering, which is in the end of the year, when thou hast gathered in thy labours out of the field.” The Holy Ghost is the power to help us get the harvest in. He is a harvesting Holy Ghost.