A.T. Robertson Commentary Revelation 21:6

"And he said unto me, They are come to pass. I am the Alpha and the Omega, the beginning and the end. I will give unto him that is athirst of the fountain of the water of life freely." — Revelation 21:6 (ASV)

They are come to pass (Γεγοναν). Second perfect active indicative of γινομα with -αν for -ασ. See 16:17 for a like use of γεγονεν, "They have come to pass." Here again it is the voice of God because, as in 1:8, He says:

I am the Alpha and the Omega (Εγω το Αλφα κα το Ο) with the addition "the beginning and the end" (η αρχη κα το τελος), the whole used in 22:13 of Christ. In Isa 44:6 there is something like the addition, and in Col 1:18; Revelation 3:14 η αρχη is applied to Christ, while here God is the First Cause (αρχη) and the Finality (τελος) as in Ro 11:36; Ephesians 4:6. But God works through Christ (John 1:3; Hebrews 1:2f.; Colossians 1:12–20). God is the bountiful Giver (James 1:5,17) of the Water of Life. See 7:17; 22:1,17 for this metaphor, which is based on Isa 55:1. It is God's own promise (Εγω δωσω), "I will give."

Of the fountain (εκ της πηγης). For this partitive use of εκ see Mt 25:8, without εκRevelation 2:17.

Freely (δωρεαν). See Mt 10:8; John 4:10; Romans 3:24; Acts 8:20; Revelation 22:17.