Jesus said, “Let anyone who is thirsty come to me, and let the one who believes in me drink. As the scripture has said, ‘Out of the believer’s heart shall flow rivers of living water.’” Now he said this about the Spirit, which believers in him were to receive; for as yet there was no Spirit, because Jesus was not yet glorified. – John 7:37-39
There are two passages on living water in the Gospel of John. In John 4, Jesus uses the term to talk primarily about eternal life. Jesus said, “4:10 If you knew the gift of God, and who it is that is saying to you, ‘Give me a drink,’ you would have asked him, and he would have given you living water.” When we partake (drink) of what Jesus is providing – or in other words, when we believe in him – we will receive living water (and eternal life).
Today, Jesus mixes that metaphor. He still speaks about a spiritual (not physical) thirst that goes deep into every human soul. And he invites everyone who has this spiritual thirst to, essentially, drink from me (to partake of his teaching and truths) until that spiritual thirst is satisfied by one’s “believ[ing] in me.” And when we believe, continues Jesus, a spiritual fruit will be produced – “out of the believer’s heart shall flow rivers of living water.” Now, in John 4, living water represented eternal life. Out of my heart – imperfect believer that I am (or you are) – cannot flow eternal life. That flows from God, not from us. So what flows out of a believer’s heart, according to this new version of this wet metaphor, is the Holy Spirit. (Jesus says precisely that.) Indeed, when we first believe, we are first filled with the Spirit. Then as we grow and grow in that grace, the Spirit can overflow from our hearts into a darkened world – ‘Out of the believer’s heart shall flow [the Holy Spirit, like] rivers of living water.’