Upanishads say you cannot experience God. If you experience God, then the God remains separate and you remain separate, because only the other can be experienced. Experience divides. This is the deepest message of all the Upanishads – experience divides. Because whenever you say experience, it means there three things, the experiencer, the experienced, and the relationship between the two, the experience.
Upanishads say the God cannot be known, because knowledge divides the knower, the known and the knowledge. If really you have become one, how can you experience? So even the experience disappears.
Upanishads say a person who claims he has experienced the divine is false; his claim proves that he is false. A knower cannot claim, one who has really experienced the divine cannot claim, because the very experience disappears.
Upanishads says that the divine can be defined only by negatives, so they go on negating. They say, ‘This is not Brahman, that is not Brahman.’ And they never say directly, they never assert directly. You cannot point to the Brahman with a finger, because your finger will become a limitation. Then Brahman will be where you finger is pointing and nowhere else. You can point to the Brahma only with a closed fist, so you are not pointing anywhere; or – everywhere.
(Source: Vedanta: The Supreme Knowledge page 77, 107 – 108)