Most of the Upanishads talk about Brahman as self-illuminating light. Self-realization is not an external factor to be witnessed. The Brahman can be compared to the sun. In the presence of sun, we are able to see neither the moon nor the stars. Sun is self illuminating and we need no light to see the sun. Imagine a situation without sun. Nothing can be seen in this earth and nothing will grow. But this sun gets its illumination from the Brahman. Without the presence of Brahman sun cannot exist. But there is a difference between the light of the sun and self illuminating Brahman. Apart from sun deriving its source of light from the Brahman, Brahman also gives knowledge to know our inner self. Sun gives light to understand the external objects whereas the Brahman which is self illuminating gives light to realise the Brahman within. Ramakrishna Paramahamsa says that the self illuminating nature of the Brahman is a situation between light and darkness. This situation can only be realized and not seen.
We cannot physically see certain things such as love, happiness, etc. Though they are not present as objects, they are there to be realized and enjoyed. Therefore, it is clear that Brahman need to be realized for attaining bliss. What is the source of jiva or soul? It is made up of mind and prana. Then what is Brahman? It is everything. There is a story about soul and Brahman. There were two birds sitting on a tree. One bird was eating fruits of the tree and another bird was enjoying the scene of the first bird eating the fruit, without itself eating it. The second bird was a witness to the activities of the first bird. The first bird is compared to soul and the second bird is compared to the Brahman. There are several such examples spread across in the scriptures and Upanishads. What we need is the time and mind. Though we have both, we do not have dedication and will power. This is where meditation is recommended. Mundaka Upanishad gives a brief description of the Brahman. It is bigger than the biggest and smaller than the smallest. It is far away from us, yet nearer to us. This cannot be realised through our senses but only through our knowledge.
The knowledge about Brahman can be attained only through our internal search. We will get answers to our internal search only in the meditation. Meditation does not mean that we have to strain our physical body. This does not yield results. Doing meditation with the sole purpose of realising the Brahman alone yields results. It is not necessary that you should sit in a particular place for days together, but concentration and dedication are important. If you do not have a strong and healthy physical body, realisation becomes difficult. Realization is possible only if our mind is without the influence of our senses. Senses rely on external factors and objects. The inputs from the senses to the mind cause Impressions in our subconscious mind. Once these impressions are formed, it is difficult to remove them. That is why internal search for the Brahman is advised, though Brahman exists everywhere.