The ascending Christ promised the descending Holy Spirit. When He ascended to the Father, He poured out His Spirit, His very Self. According to Peter in Acts 2, the Holy Spirit is poured out by the crucified, risen and exalted Christ. Jesus said, “I will not leave you, I will come to you.” The Holy Spirit is Christ unleashed in the world. He is subversively present where He is not wanted. He is intimately present where He is welcomed.
“And behold, I am sending the promise of my Father upon you. But stay in the city until you are clothed with power from on high.” Then he led them out as far as Bethany, and lifting up his hands he blessed them. While he blessed them, he parted from them and was carried up into heaven. And they worshiped him and returned to Jerusalem with great joy, and were continually in the temple blessing God. Luke 24:49-53 (ESV)