No one can say with finality that God is only 'this' and nothing else. He is formless, and again He has forms. For the bhakta He assumes forms. But He is formless for the jnani, that is, for him who looks on the world as a mere dream.

The bhakta feels that he is one entity and the world another. Therefore God reveals Himself to him as a Person. But the jnani - the Vedantist, for instance -always reasons, applying the process of 'Not this, not this'. Through this discrimination he realizes, by his inner perception, that the ego and the universe are both illusory, like a dream. Then the jnani realizes Brahman in his own consciousness. He cannot describe what Brahman is.

Reference: The Gospel of Sri Ramakrishna (6.1 The Master With The Brahmo Devotees (I))