The mind must be raised higher and higher to a state where all thoughts are checked. The state is called Samadhi.
When all activities of the mind cease, what remains, what shines by itself, is the Truth, the Self, the Supreme Self.
It is impossible to explain Samadhi or the Self that is of the nature of Samadhi, so as to make it intelligible to others. Experience alone can make any person to understand it.