The promise of the Holy Spirit can be broadly traced back to what God promised through Ezekiel13. It’s then announced by John the Baptist1 and Jesus2. It first unfolds with Jesus’ promise of the Holy Spirit (e.g. “Helper”) to the apostles in the upper room3, and He repeats it again to them after His resurrection4,5,6. This promise to the apostles includes both guidance into “all truth”3,4,5,6 but also an outward manifestation of power7,8 to confirm their word with miracles. “Not many days” later, on the day of Pentecost, they would experience the “baptism of the Holy Spirit” for the first Jews7 (and once more for the first Gentiles).
But God’s promise of the Holy Spirit was for all that obeyed Him13, and that’s what Peter tells the crowd that was responding to the gospel message9 for the first time. This is the “Spirit part” of what Jesus shared with Nicodemus2 for those born again. It is the “indwelling of the Holy Spirit” for all/any (e.g. Jew or Gentile12) that would respond to the gospel12 in baptism2,9 and obedience10,11,13.