"The river of the water of life is symbolic of a profuse and constant flow of life, of the continuous operation of the life-giving spirit of God in Christ and in all who are made one in Him. The glorified saints receive and appropriate this divine flow of life, and they also become a source of its life-giving properties for all men and all creation."
Much more in the link:
https://www.godfire.net/eby/Rev/rev248.html
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On the cross, Jesus paid for the sins of all the people in the world, so perhaps the cross IS the throne, the place of authority--He owns us all. And Oh look, out from His side flowed blood and WATER -the river. Now we can come to Him and drink.