When the Holy Spirit came on the day of Pentecost, the disciples did not actually know what to expect. They only knew what Jesus said, that the gift would come and that power from the Holy Spirit would be given. Much to everyone's surprise, the Spirit came like a whirlwind and fire with the disciples all speaking in tongues. Those who spoke against the work of the Spirit did not understand the Holy Spirit. The gift is the Holy Spirit and He has given us power for Christ's mission.