Before his Passover, Jesus told the Apostles that he would ask the Father to send another Advocate to be with them, the Spirit of truth, the Holy Spirit. On Pentecost, the Holy Spirit descended on the Apostles, and filled them with the fortitude to go out and preach the Gospel to the whole world.
Not only did the Holy Spirit embolden the Apostles, the entire scripture is inspired by the Holy Spirit. This is the Father speaking through the Spirit. Since the Holy Spirit proceeds from the Father and the Son through love as the author of grace, the Spirit shares the grace and love of the Father and Son with each of us.