I was shown the river of life-giving water on either side of which grew the tree of life. These words will sound familiar to him/her who reads the Scripture. While today they come to us from the Book of Revelation, one would ordinarily see them as coming from the famous vision of the Spring in the Temple which we find in the Book of Prophet Ezekiel (cf. Ezekiel 47:1-12). The two accounts are so similar in details that one can be excused for conflating the two. And understandably so, for both are visions that focuses on the end-times.
In the passage we read for today, John is writing to a people (his community) who have undergone persecution and suffering because of their faith. Living at a period that was considered the end time (there was a belief that the second coming of the Christ was imminent for two reasons: Jesus had been misunderstood to have said that the last apostle would not die before his second coming [cf. John 21:22]; secondly, in the literature of the end times which this community must have been familiar with, the second coming of Christ is preceded by persecution of the faithful, similar to what they were undergoing), the believers in John’s community needed some encouragement. As such, in contrast to what surrounded them (death and decay), John paints to them a picture of heaven - where there is life and light, no more death and darkness - in an attempt to encourage them. It is a depiction that is aimed at giving them hope to remain strong and steadfast in their faith. They needed to remain steadfast in their faith because the situation in which they had suddenly found themselves was short-lived and would soon be replaced by everlasting happiness. 
But it is also important to note that the vision comes at the end of the Book of Revelation, the last book in the bible. A closer look at the vision will show a similarity to the Garden of Eden in Genesis (tree of life, the river). Unlike the garden in the Genesis creation account that became the source of creations’ downfall and death, this new garden is life-giving. In this new Garden, new creation will not be separated from God for they will constantly be looking upon God’s face. It is thus a vision that makes right what became flawed at the beginning of creation.