Verses 12-14 of the Isha Upanishad mirror in their framing verses 9-11. The earlier verses referred to Knowledge and Ignorance. The latter verses describe Birth and Non-Birth in parallel fashion.
“Into a blind darkness they enter who follow after the Non-Birth, they as if into a greater darkness who devote themselves to the Birth alone. Other, verily, it is said, is that which comes by the Birth, other that which comes by the Non-Birth; this is the lore we have received from the wise who revealed That to our understanding. He who knows That as both in one, the Birth and the dissolution of Birth, by the dissolution crosses beyond death and by the Birth enjoys Immortality.”
Sri Aurobindo notes: “The Self outside Nature does not become; it is immutable as well as eternal. The Self in Nature becomes, it changes its states and forms. This entry into various states and forms in the succession of Time is Birth in Nature. … Birth and Non-Birth are not essentially physical conditions, but soul-states. A man may break the knot of the ego-sense and yet remain in the physical body; but if he concentrates himself solely in the state of dissolution of ego, then he is not born again in the body. He is liberated from birth as soon as the present impulse of Nature which continues the action of the mind and body has been exhausted. … Exclusive attachment to Non-Birth leads to a dissolution into indiscriminate Nature or into the Nihil, into the Void, and both of these are states of blind darkness. … On the other hand, attachment to Birth in the body means a constant self-limitation and an interminable round of egoistic births int he lower forms of egoism without issue or release.”
“…each of these tendencies, pursued with a certain relativeness to the other, has its own fruit and its own good. Non-Birth pursued as the goal of Birth and a higher, fuller and truer existence may lead to withdrawal into the silent Brahman or into the pure liberty of the Non-Being. Birth, pursued as a means of progress and self-enlargement, leads to a greater and fuller life which may, in its turn, become a vestibule to the final achievement. But neither of these results is perfect in itself nor the true goal of humanity. Each of them brings its intended portion into the perfect good of the human soul only when it is completed by the other.”
“The realisation of the Self as the unborn and the poise of the soul beyond the dualities of birth and death in the infinite and transcendent existence are the conditions of a free and divine life in the Becoming. The one is necessary to the other. It is by participation in the pure unity of the Immobile (Akshara) Brahman that the soul is released from its absorption in the stream of the movement. So released it identifies itself with the Lord to whom becoming and non-becoming are only modes of His existence and is able to enjoy immortality in the manifestation without being caught in the wheel of Nature’s delusions.”
“Thus by dissolution of ego and of the attachment to birth the soul crosses beyond death; it is liberated from all limitations in the dualities. Having attained this liberation it accepts becoming as a process of Nature subject to the soul and not binding upon it and by this free and divine becoming enjoys Immortality.”
Sri Aurobindo, The Upanishads, Isha Upanishad and analysis, pp. 21-23, 28 & 51-73