The disciples returned to Jerusalem, as Jesus instructed them, to wait for the Comforter or the Holy Spirit. During this time they chose Matthias as an apostle to fill the place of Judas Iscariot.
On Pentecost the Holy Spirit was poured out upon the disciples, audibly as the sound of a mighty rushing wind and visibly as tongues as of fire. The disciples began to speak in tongues and proclaimed Christ. That day 3000 were pricked in the heart, repented and were baptized.
That the Lord would prick us in the heart and that the cry, 'What must we do to be saved', would yet be heard today.