The nature of water is to run down. The water of the ocean stands there itself as a vast mass. The ocean is the lowest place on earth. Therefore, the water in the ocean has no place to run down. But, when water is evaporated by the sun and transformed into clouds, it never stands still in the sky.
Driven away by the winds to mountain tops, cooled and transformed into pure water, it runs. As per the nature of water it again starts flowing down seeking for its source in waterfalls, gathers into many streams, runs down to lower places as river and finally merges again into its source, the ocean. In no way it can be stopped till it reaches its source, the ocean. Though it may flow into many channels and irrigate fields or be collected in lakes and tanks or be stopped by springs and wells, it will not remain there for long; for, it evaporates again, is transformed into clouds and tries to reach its source as before!
The efforts that we observe as in the life of jeevas, individual souls, are exactly like this! The source of all jeevas, not only humans but of all creatures is the Supreme Thing (Brahman). The innumerable souls living in innumerable globes which, because of an indefinable wondrous power appear to be separated from their source, are ever hurrying back to the Supreme, their source. Just as running down towards the lowest place is the nature of water, the effort observed in jeevas in the form of thoughts, speech and actions to return to their source, the Supreme, is verily the nature of jeevas. Hence the aim of all jeevas is to return to their source, Brahman.
Source: ~ In: The Path of Sri Ramana - Part Two - Chapter 2: Love or Bhakti.