True human unity depends on the psychological unity of humanity. The watchwords of liberty, equality and fraternity express basic truths of the relationship of all human beings with one another, and they alone can, in their fulfillment, provide the basis for human unity.
Sri Aurobindo notes: “Yet is brotherhood the real key to the triple gospel of the idea of humanity. The union of liberty and equality can only be achieved by the power of human brotherhood and it cannot be founded on anything else. But brotherhood exists only in the soul and by the soul; it can exist by nothing else. For this brotherhood is not a matter either of physical kinship or of vital association or of intellectual agreement. When the soul claims freedom, it is the freedom of its self-development, the self-development of the divine in man in all his being. When it claims equality, what it is claiming is that freedom equally for all and the recognition of the same soul, the same godhead in all human beings. When it strives for brotherhood, it is founding that equal freedom of self-development on a common aim, a common life, a unity of mind and feeling founded upon the recognition of this inner spiritual unity. These three things are in fact the nature of the soul; for freedom, equality, unity are the eternal attributes of the Spirit. It is the practical recognition of this truth, it is the awakening of the soul in man and the attempt to get him to live from his soul and not from his ego which is the inner meaning of religion, and it is that to which the religion of humanity also must strive before it can fulfil itself in the life of the race.”
Sri Aurobindo, The Ideal of Human Unity, Part Two, Chapter 34, The Religion of Humanity, pg. 300