The self is not only not seeable. You can't hear it, smell it, taste it, touch it, nor do any of the you know the extremely sensitive instruments which we have designed. Nachak susha pashchitikaschanaynam. So not by the eyes is it ever seen by anybody. It is not an object for you know it cannot be objectified by the senses. And then here he says, nasandri shet istatirupa masya.
Swami Sarvapriyananda teaches the Katha Upanishad, one of India's most revered texts which is also a part of the Vedas. It is a collection of philosophical poems representing a conversation between the sage Naciketas and Yama (god of death). They discuss the nature of Atman, Brahman and Moksha(liberation).