When we speak of spiritual union or mystical union with Christ, we must be careful not to fall into heretical forms of mysticism. In Eastern forms of mysticism the religious goal is a kind of unity (unio) with the deity by which the individual is so absorbed by the ‘ultimate one’ that personal identity is obliterated. In Christian mystical union, the self is not lost or erased by being merged with some oversoul or universal essence.
R.C. Sproul