First of all, he must be just and severed from all else save God; his heart must be entirely turned to the supreme horizon; he must be free from the bondage of self and passion, for all these are obstacles.
(‘Abdu’l-Bahá, Some Answered Questions, p. 38)
For the spirit and the soul of Adam, when they were attached to the human world, passed from the world of freedom into the world of bondage, and His descendants continued in bondage. This attachment of the soul and spirit to the human world, which is sin, was inherited by the descendants of Adam, and is the serpent which is always in the midst of, and at enmity with, the spirits and the descendants of Adam. That enmity continues and endures. For attachment to the world has become the cause of the bondage of spirits, and this bondage is identical with sin, which has been transmitted from Adam to His posterity. It is because of this attachment that men have been deprived of essential spirituality and exalted position.
(‘Abdu’l-Bahá, Some Answered Questions, p. 123-124)
Souls, that is, who will consign their own selves to oblivion, strip from themselves the defects of humankind, and unchain themselves from human bondage, will beyond any doubt be illumined with the heavenly splendours of oneness, and will all attain unto real union in the world that dieth not.
(‘Abdu’l-Bahá, Selections from the Writings of ‘Abdu’l-Bahá, p. 117)