This fundamental gift of the Holy Spirit—whom Jesus called the “promise of the Father”—was given to the apostles at Pentecost. And in the miraculous events that accompanied the sending of the Holy Spirit, it became quite clear that the saving action of God would compellingly move forward. Those present in the Upper Room were recreated according to the order of grace to share the life of God, who is love. They were able to, as it were, “breathe with God.” This love poured into their hearts by the Holy Spirit is no mere human sentiment but the indwelling presence of the divine. It courses through them as gently and imperceptibly as the air they breathe. The Holy Spirit is the unseen power that fuels the ministry and activity of the apostles and gives them the courage to speak in Jesus’s name.
— from the book Inspired: The Powerful Presence of the Holy Spirit by Fr. Gary Caster