Imperishable it is
न जायते म्रियते वा कदाचिन् नायं भूत्वा न भविता वा न भूय:। अजो नित्य: शाश्वतोऽयं पुराणो न हन्यते हन्यमाने शरीरे॥
na jāyate mriyate vā kadācin nāyaṁ bhūtvā bhavitā vā na bhūyaḥ ajo nityaḥ śāśvato 'yaṁ purāṇo na hanyate hanyamāne śarīre
Neither is it ever born, nor does it ever die Neither is it recreated as body is born Birthless, eternal, unaltering, timeless it is Imperishable it is in the perishable body.
Needless to say, it is the soul which is being talked about here. I sometimes wonder what do they mean by soul? How is it imperishable. The reason I love this shloka (and Gita in general) is that it leaves a scope open for thought and interpretation. I feel that it is the law of nature which is the soul. Unaltered, unborn, unchanging. It manifests itself as everything that surrounds us. And unaffected by the death and birth of the bodies, it persists as the imperishable. The bodies come and go just leaving a mark on the evolution of universe.