2-19, 20 Sankhya Yoga (सांख्य योग) 19 & 20th verses

य एनं वेत्ति हन्तारं यश्चैनं मन्यते हतम् |
उभौ तौ न विजानीतो नायं हन्ति न हन्यते ||(2-19)||

ya enaṁ vetti hantāraṁ yaśh chainaṁ manyate hatam
ubhau tau na vijānīto nāyaṁ hanti na hanyate

Word to Word Meaning: yaḥ—one who; enam—this (atma in his body); hantāram—the slayer; vetti—knows;  yaḥ—one who; cha—and; enam—this (atma in his body); manyate—thinks; hatam—slain; tau they; ubhau—both;  na—not; vijānītaḥ—in knowledge; na—neither; ayam—this (atma); hanti—slays; na—nor; hanyate—is killed. 

Literal Meaning: Whoever thinks of the eternal (atman) as the slayer or the one who is slain, neither of them are in appropriate knowledge. The truly eternal (atman) is not subject to change. 

न जायते म्रियते वा कदाचि
नायं भूत्वा भविता वा न भूय: |
अजो नित्य: शाश्वतोऽयं पुराणो
न हन्यते हन्यमाने शरीरे ||(2-20)||

na jāyate mriyate vā kadāchin
nāyaṁ bhūtvā bhavitā vā na bhūyaḥ
ajo nityaḥ śhāśhvato ’yaṁ purāṇo
na hanyate hanyamāne śharīre 

Word to Word Meaning: ayam—this (atma); kadāchit—at any time; na jāyate—is not born; na mriyate—not dies; vā—or;  na—not; bhūtvā—having once existed; bhūyaḥ—further; bhavitā vā na —will not manifest in future as well; ayam—this (atma); ajaḥ—unborn; nityaḥ—eternal; śhāśhvataḥ—immortal; ayam—this (atma); purāṇaḥ—the most ancient; na hanyate—is not destroyed; śharīre—when the body; hanyamāne—is destroyed; 

Literal Meaning: This soul is never born. It will never die. He does not manifest with reference to certain time frame.  He is without birth. Eternal. Ageless. It is not destroyed when the body is destroyed.

Commentary: The Atma is within us but remains unknown. This theme is repeated several times in the Bhagavad Gita. The path to self-realization is through meditation. All other pursuits will lead us into ignorance.