Read: John 7:25-52
On the last and greatest day of the festival, Jesus stood and said in a loud voice, Let anyone who is thirsty come to me and drink. Whoever believes in me, as Scripture has said, rivers of living water will flow from within them. By this he meant the Spirit, whom those who believed in him were later to receive. Up to that time the Spirit had not been given, since Jesus had not yet been glorified. (John 7:37-39)
John is writing this gospel after the day of Pentecost when the Spirit was given in great power and came into the hearts of believers. When Jesus was still on earth the Spirit had not yet been given in that way. The Spirit of God is always present everywhere in the world. He was present before the day of Pentecost as well as afterward. But not in this sense. He was not performing this ministry of making Jesus real. So for the first time we have our Lord’s hint of how this is all going to be accomplished. I must leave, I am going back to him who sent me, but when I do so I will send the Spirit. He goes on and teaches what that means by using a beautiful symbol.