He said: 'The person that is seen in the eye, that is the Self. This is the immortal, the fearless, this is Brahman. Even though they drop melted butter or water on him, it runs away on both sides.

In plain words: The teacher tells Upakosala that the person seen in the eye is the true Self. It cannot die and has nothing to fear, and it is Brahman, the ultimate reality. Like an eye that stays clean when butter or water drips on it, the Self is untouched by anything.