By perceiving the impressions, (comes) the knowledge of past life.
In plain words: Every experience leaves a faint mark, or impression, in the mind that never fully disappears. By focusing deeply on these impressions, a yogi can remember his past lives.
Each experience that we have, comes in the form of a wave in the Chitta, and this subsides and becomes finer and finer, but is never lost. It remains there in minute form, and if we can bring this wave up again, it becomes memory. So, if the Yogi can make a Samyama on these past impressions in the mind, he will begin to remember all his past lives.
Namaste.
A calm guide to life, the mind and the old teachings.