St. Hilary begins to interpret Revelations 22:1:
Bodily manifestations so reveal the mysteries of heaven that, although matter by itself cannot convey the full spiritual meaning, yet to regard them only in their material aspect is to mutilate them. We should have expected to hear that there were trees, not one tree, standing on either side of the river shewn to the saint. But because the tree of Life in the sacrament of Baptism is in every case one, supplying to those that come to it on every side the fruits of the apostolic message, so there stands on either side of the river one tree of Life. There is one Lamb seen amid the throne of God, and one river, and one tree of Life: three figures wherein are comprised the mysteries of the Incarnation, Baptism and Passion, whose leaves, that is to say, the words of the Gospel, bring healing to the nations through the teaching of a message that cannot fall to the ground.
Note how St. Hilary plays with idea and number of one. There is one tree, one river, one Lamb — one Incarnation, one Baptism and one Passion. In other words, Christ and His Church are the answer to the multitude, the balkanization, and the conflict among the nations. As St. Paul says in Colossians 3:11:
Here there cannot be Greek and Jew, circumcised and uncircumcised, barbarian, Scythian, slave, free man, but Christ is all, and in all.
The Greeks and Jews represent the known world of the early Church. The barbarian and Sythian represent all of those people that live beyond the borders of the Roman Empire and the known world. Thus, Christ embraces and wishes to unite the whole world in Himself.
In contrast, it is interesting to look at the Greek word for devil — διάβολος. It is a compound word which literally means the one who throws through. Imagine for moment two people talking to each other in a close relationship. If one throws something through them — putting something in-between them — it interrupts the conversation and the relationship. In other words, the devil is the one who divides.
This is a good litmus test for discerning whether something comes from God or the Evil One: will it unite or divide? This is why, when one reads the canons of the Ecumenical Councils, the Church has worked so hard not only to hold onto the dogmas as they have been passed down through generation after generation, but on how to provide pastoral ways for both schismatics and even heretics to come back into the Church. As the Body of Christ our job is not judgement — not to determine who is saved and who is not — but rather to unite all the nations under the banner of Christ and His Church.