What does the author mean when he writes, "Man is the only one who is alone"?

When the author states that man is the only one who is alone, he puts man in the context of all creatures in the world. Out of all the creatures, only man knows that he is alone, and therefore seeks companionship. Paz puts man's existence in terms of the supernatural. Man was somehow not alone before he lived on Earth, and it is quite possible that he will not be alone after he dies. Only the middle portion of his life, on earth, separates him both from fellow men and from the being whom he formerly was.