Pentecost or the descent of the Holy Spirit is celebrated by millions of Christ's followers around the world. The question is, why do we Christians celebrate Pentecost? On Pentecost, we are reminded of the moments when the Holy Spirit came to earth: After Easter, the disciples were gathered together in a great house in Jerusalem, when suddenly a voice came from heaven. A sound like the wind and the storm that filled the whole house. The disciples were filled with the Holy Spirit and felt great strength and power within themselves.