97 Earlier, John’s Gospel had spoken of this event, when on “the last day of the festival” ( Jn 7:37), Jesus cried out to the people celebrating the great procession: “Let anyone who is thirsty come to me and drink… out of his heart shall flow rivers of living water” ( Jn 7:37-38). For this to be accomplished, however, it was necessary for Jesus’ “hour” to come, for he “was not yet glorified” ( Jn 7:39). That fulfilment was to come on the cross, in the blood and water that flowed from the Lord’s side.
Source: Dilexit Nos (Vatican.va)