The Greek ekporeuomai means to go out, proceed, or come forth from a source. It is used of rivers flowing out (Revelation 22:1), the words proceeding from God's mouth (Matthew 4:4 quoting Deuteronomy 8:3), the Spirit who 'proceeds from the Father' (John 15:26 β one of the most theologically significant uses in church history), and of multitudes coming out to be baptized by John (Matthew 3:5).
John 15:26 β 'the Spirit of truth who goes out (ekporeuomai) from the Father' β became the central term in the Filioque controversy between Eastern and Western Christianity (does the Spirit proceed from the Father alone, or from the Father 'and the Son'?). Regardless of that later debate, the verse establishes the Spirit's divine origin and mission: He comes from the Father and is sent by Jesus. Ekporeuomai in Revelation 22:1 β the river of the water of life proceeding from the throne of God and of the Lamb β shows the Spirit's life-giving work flowing through all of new creation.