Sri Aurobindo translates Katha Upanishad, Second Cycle: First Chapter, Verses 14-15: “As water that rains in the rough and difficult places, runs to many sides on the mountain-tops, so he that sees separate law and action of the One Spirit, follows in the track of what he sees. But as pure water that is poured into pure water, even as it was such it remains, so is it with the soul of the thinker who knows God, O seed of Gautama.”
The first image of the water running to many sides illustrates the normal action of the mind running after all the objects of the senses, constantly changing and having a dispersed action. The mind observes and acts upon fragmented elements of difference, and the individual chases after what he sees in a phantasmagoria of objects of desire, goals and wishes. The ‘water’ is broken up into many troubled streams of movement. The action is weakened due to the dispersion of energy across many different objects and actions. This represents then the human standpoint of experience.
The second image of the pure water poured into pure water, without undergoing change in its nature, represents the unity of the soul with the divine Soul. This represents the divine standpoint of experience. The water here is calm and untroubled, as also the view of the individual who knows his Oneness with the Divine.
Sri Aurobindo, The Upanishads, Katha Upanishad, pp. 213-241, and Kapali Sastry, Lights on the Upanishads, pp. 104-129