Dvaitadvaita is a philosophy in Hinduism affirming both dualism and non-dualism of atma and Paramatma. It maintains that Brahman and atman (soul) are unchangeable and unaffected by the passions like joy or sorrow. This immutable position of atman qualifies it to merge totally with Brahman.
Swami Vivekananda states that Advaita School of thought harmonizes both the concepts – dvaita and advaita – to lead to Dvaitadvaita.
A seer achieves union of this atman or soul with the Brahman and becomes free from the cycle of birth and rebirth. The theory of Dvaitadvaita enables a sage or wise man to transform the manas into thought activity and creates the seeming changeful appearance.
The change in manas produced the world of appearances which is illusory. It is not eternal. It is subject to pain and joy of the sense. The experience of pleasure or sorrow is conceptual in as much as it is produced by ignorance of the Ultimate Truth attainable through synthesis with the Over-arching Soul.
The state of Dvaitadvaita does not express any intrinsic joy or pain. It helps seeking release of atman through the recognition of its root-cause.
The Dvaitadvaita view germinates in the bhashyas of Sri Adi Shankaracharya which question the dualism of the Dvaita view, the division of the world of senses and Brahman as two distinct areas of reality.
Dvaitadvaita seeks to establish the truth of oneness of the self-soul with Brahman. The Ultimate Truth dawns when the devotee achieves the understanding of the Dvaita Advaita bhava.
Source - Notes taken from Encyclopedia of Hinduism Volume III - page 565 - IHRF - Rupa - 2011