38 He who believes in Me, as the Scripture has said, out of his heart will flow rivers of living water.”
38 He who believes in Me,
Belief is the means of coming to Christ. The Greek carries the idea of continued trust in Christ (present participle). The idea is not initial salvation but the ongoing believer’s life.
as the Scripture has said,
Reference to “Scripture” here may not refer to any particular passage but to an accumulation of passages such as Zechariah 14:8 (Ps 46:4,5; Is 44:3; 55:1; 58:11).
out of his [the believer’s] heart will flow rivers [streams] of living water.”
Streams of living water refers to the provision of eternal life from the Holy Spirit. There is no trickle here. The person who drinks of Christ will never thirst again. Everyone who drinks of Christ will become a fountain, a constant supply of the water of life for others through the Holy Spirit. Christ is the living water and those who believe on Him have Christ formed in them. People who believe in Jesus will be a source of blessing for others through the Holy Spirit (see next verse).
The idea of this phrase is that God gives blessing not only to the believer but that He is also a source of blessing to others.
When a person believes on Christ, the Holy Spirit immediately engages with him.
A genuine believer is not self-centered. The moment he or she believes in Christ, immediate effects result. He or she becomes a channel of blessing to others. Jesus is the source of blessing, but the believer is the channel of that blessing by the power of the Holy Spirit.
Jesus offered two blessings to the believer. First, He offered Himself as a source of satisfaction for the believer’s soul. Second, He gave the believer to be a source of blessing to others by the indwelling Holy Spirit; that is, Jesus’ followers will become channels of spiritual life. His grace and blessing will flow through people who engage with Him. This blessing will not be meager but will be abundant like rivers of living water. The believer is not the blessing but the channel of blessing.