In the previous chapter, John was shown a new order of things. An entirely new heaven and earth were created to replace the first heaven and earth which fled away at the Great White Throne Judgment (Rev. Rev. 20:11+). In addition to the new heaven and new earth, John saw the holy city, the New Jerusalem, descending from heaven as a bride for the Lamb (Rev. Rev. 21:2+, Rev. 21:9+). Johns vision was given in two parts. The first part provided an overview of the eternal order (Rev. Rev. 21:1-8+). In the second part, an angel accompanied John on a more detailed tour of the New Jerusalem, providing additional information and measurements of the city. In many ways, the chapter break at Revelation Rev. 21:27+ is unfortunate because the first five verses of this chapter should really be considered as the conclusion of Johns detailed tour of the New Jerusalem.
he showed me
This is the angel who first accompanied John in the Spirit to show him the holy Jerusalem, descending out of heaven from God (Rev. Rev. 21:10+). This is one of the angels having the seven bowls filled with the seven last plagues (Rev. Rev. 21:9+). It may be the same angel which took him in the Spirit to see the great harlot, Babylon (Rev. Rev. 17:3+). The tour contrasts the New Jerusalem, the city of God, with Babylon, the city of man.
a pure river of water of life
This is the fountain of the water of life which God promised to the thirsty in the previous chapter (Rev. Rev. 21:6+). Its ultimate source is God Himself, for it proceeds from His throne (cf. Ps. Ps. 36:8-9; Ps. 46:4).
A similar river will flow from under the threshold of the Millennial Temple (Eze. Eze. 47:1-2; Zec. Zec. 14:8), but that river does not reach all regions, so sin remains in the Millennium (Eze. Eze. 47:11). Now, sin is no more and life abounds in all parts of the new creation. See commentary on Revelation 7:17, Revelation 21:6, and Revelation 22:17.
clear as crystal
The purity and clarity of the water is remarkable to John. The clarity speaks of sinlessness and symbolizes the cleansing from sin of those who partake of the river. Although this is a literal river in the eternal state, it also typifies the Holy Spirit Who cleanses and gives life to those who trust Christ in this age (John John 4:10; John 7:37-38). In the eternal state, there is no more death because there is no more sin (Rev. Rev. 21:4+).
When John first ascended to the throne room in heaven, he saw the sea of glass like crystal, in the midst of the throne (Rev. Rev. 4:6+). The sea of glass probably symbolized this river which would be the basis of cleansing and eternal life in the new heaven and earth. Although the nations will partake of the tree of life, the tree itself draws from this river of life (cf. Ps. Ps. 1:3).
proceeding from the throne of God and of the Lamb
The river proceeds from the throne because the source of all life is ultimately God (Job Job 33:4; Eze. Eze. 37:9; John John 1:4; John 14:6; Acts Acts 3:15; Rev. Rev. 11:11+).
There is no sea from which waters are raised by the sun, as in the present hydrologic cycle (Rev. Rev. 21:1+) and thus no rainfall to supply the river with its flow. Rather, it proceeds out of the throne of God and of the Lamb, high at the central pinnacle of the holy city. Evidently the mighty Creator is continually creating the waters, then sending them forth to give perpetual life and cleansing and beauty to the city and its inhabitants, and then on out into the uttermost parts of the new earth.1The throne is of God and of the Lamb. In the eternal state, there is no more distinction between the throne of the Father in heaven and that of the Son on earth (Mtt. Mat. 25:31; Rev. Rev. 3:21+). Jesus rules from the Davidic throne during the Millennial Kingdom until the last enemy, death, is destroyed (Rev. Rev. 20:14+). Then, He delivers the kingdom to God the Father (1Cor. 1Cor. 15:24-26) and the throne of David merges with the heavenly throne of the Father (Rev. Rev. 22:3+) and both the Father and the Son continue to rule forever.
On Jesus as the Lamb, see commentary on Revelation 5:6.