Brahmajyoti means combination of all the living entities, the spiritual sparks. To become one with the brahmajyoti means... Just like one bird enters into the green tree. It appears that it has become one. The tree is also green and the bird is also green. So when the bird enters the tree, it appears that the bird is now mixed up. But that is not the fact. The bird keeps his individuality, and at any time, when he wants, he can come out of the tree and fly anywhere. That independence is there, although apparently it seems that he has become one with the tree. Similarly, the sayujya-mukti means apparently he is in Brahman, but factually it is not. Because each individual soul is different.
Lecture on Bhagavad-gita 7.3, Vrndavana, 31 October, 1973