“If anyone thirsts, let him come to me and drink. He who believes on me, as the Scripture has said, out of his inner being will flow rivers of living water.”
At such a time, reference to flowing water would immediately bring to people's minds the water poured out daily before God at the Temple, symbolising rain and fruitfulness, and the coming deliverance. Their minds were full of it. Thus the ‘birth from above, birth from water' (John 3:6) is here seen in the spiritual rain which would feed the spiritual springs and provide plentiful water for the people to drink. It will result from response to His words. In the words of His previous preaching, ‘he who believes in Me will never thirst' (John 6:35). And this would be associated in the minds of the people with the ‘drawing of water from the wells of deliverance' (compare also John 4:13-14).
But now a new promise was added. ‘He who believes on me, as the Scripture has said, out of his inner being will flow rivers of living water.' This went beyond what had been taught before. Now they were not only to receive life but were to expect to be purveyors of that life to the world. It was a promise that the great outpouring of the Spirit promised by the prophets was approaching, resulting in rivers of water for all. What John's baptism pointed to was about to be fulfilled.
So now Jesus was promising something even greater than previously. Men had been told that they could be born from above, and drink of the water of life through putting their full trust in Jesus, but now was added the concept that they would then become the source of life to others. Water would flow out from them to others, just as in Ezekiel 47:1 onwards it was to flow from God's Temple to the world (compare Joel 3:18). This is what was to come. Those who responded would become a new Temple and the source of life to the world.
The rebirth by the Spirit was unquestionably already taking place in men's hearts, and they were even then drinking of the water of life as they responded to the words of Jesus. That is something that must not be forgotten. From the beginning God had worked through His Spirit. But now, He was saying, there is something even more wonderful yet to come, a pouring out of the Spirit which will make them life-giving fountains to the world.