VIII: 19

Chapter 8, Verse 19

"Thus the infinity of beings,
Which live again
All powerlessly disappear
When the night of darkness comes.
They do as they must."

Swami Shivananda:

Ignorance, selfish desire and action are the three knots that bind a person to this individual existence.  People exert to obtain and enjoy the objects of their selfish desires.  During these activities, they favor some and injure others through the forces of love, hatred, attraction and repulsion.  They become caught in the wheel of worldliness and transmigration, taking birth again and again to reap the fruits of their own actions.  They come forth repeatedly and dissolve through the force of their own Karmas.

In order to create dispassion and a longing for liberation, Krishna explains how all beings come into being again and again on account of their actions caused by desires born of ignorance.

Paramahansa Yogananda:

Esoterically, the cosmic cycles refer to the inner microcosmic universe of a person's astral body, which governs individual evolution.  The spiritual eye, which receives its light and energy from its connection with the divine center of consciousness in the thousand-petaled lotus at the top of the head is the Sun of the microcosm.

In twelve-year cycles, a person slowly advances in his or her spiritual evolution.

For those who seek liberation, God sends his Avatars to show the way to hasten salvation.  Sincere Yogis, according to the degree of past-life spiritual attainments and present merit, may achieve liberation in three, six, twelve, twenty-four or forty-eight years, or in only one or a few additional incarnations.