Emptiness and Form are not-two. After you realise that the manifest world is illusory, and after you realise that Brahman alone is real, then you can see that the absolute and the relative are not-two or nondual, then you can see that nirvana* and samsara* are not-two, then you can realise that the Seer and everything seen are not-two, Brahman and the world are not-two – all of which really means, the sound of those birds singing!
