From Ellam Ondre (All is One), written in the 19th Century, by an anonymous author, in Tamil, and translated into English by K. Lakshmana Sarma, in 1951,
“All including the world seen by you and yourself, the seer of the world, is one only. All that you consider as I, you, he, she and it, is one only. What you consider to be sentient beings and what you consider to be insentient, such as earth, air, fire and water is all one.
The good which is derived by your considering all as one cannot be had by considering each as separate from the other. The knowledge of the unity of all, is good for you and good for others as well. Therefore all is one.
He who sees “I am separate,” “you are separate,” “he is separate” and so on, acts one way to himself and another way to others. He cannot help doing so. The thought “I am separate, others are separate” is the seed from which grows the tree of differing actions in relation to different persons. How can there be any lapse from righteousness for a person who knows the unity of himself with others? As long as the germ of differentiation is there, the tree of differing actions will flourish, even unawares. Therefore give up differentiation. All is one only.
Ask: “If in the world all things appear different, how can I consider all as one? Is there any way of gaining this knowledge?” The reply is: “In the same tree we see leaves, flowers, berries and branches, different from one another, yet they are all one because they are all included in the word ‘tree’. Their root is the same; their sap is the same. Similarly, all things, all bodies, all organisms are from the same source and activated by a single life principle.” Therefore all is one…
The knower of unity will act as one should. In fact, the knowledge of unity makes him act. He cannot err. In the world, he is God made visible. All is one.”