After Christ's death and resurrection, he told his disciples that he would ascend to Heaven but promised to send the Holy Spirit to them.
When the Apostles were gathered at Pentecost, the Holy Spirit came like a wind and with tongues of fire, enabling them to speak in all languages and so to spread the gospel of Christ to all nations. The crowd which had assembled were amazed at the ability of the Apostles to speak in any language (Acts 2).