In plain words
I am Ātma, Gudakesha, dwelling in the hearts of all beings. I am the beginning, the middle, and also the end of beings.
Word for word
I am the Self, O Guḍākeśa, abiding in the heart of all beings; I am the beginning and the middle and the end too of beings.
The commentators
Bhagavadgītābhāṣyam
तत्र प्रथममेव तावत् शृणु —
अहम् आत्मा प्रत्यगात्मा गुडाकेश, गुडाका निद्रा तस्याः ईशः गुडाकेशः, जितनिद्रः इत्यर्थः ; घनकेश इति वा । सर्वभूताशयस्थितः सर्वेषां भूतानाम् आशये अन्तर्हृदि स्थितः अहम् आत्मा प्रत्यगात्मा नित्यं ध्येयः । तदशक्तेन च उत्तरेषु भावेषु चिन्त्यः अहम् ; यस्मात् अहम् एव आदिः भूतानां कारणं तथा मध्यं च स्थितिः अन्तः प्रलयश्च ॥ २० ॥
In plain words
On that, before anything else, listen to this much —
I am the Self, the innermost Self, O Guḍākeśa. 'Guḍākā' means sleep, and its master is called its 'īśa' — so 'Guḍākeśa' means one who has conquered sleep; or, it can also mean 'thick-haired.' I dwell seated in the very heart, in the innermost abode, of every single being; I, the Self, the innermost Self, am always what is to be meditated on. But for anyone who cannot meditate on me directly, I can still be contemplated through everything that follows — because I alone am the beginning, the cause of all beings, and equally their middle, their continuing, and their end, their dissolution.
Close to the Sanskrit
There, first indeed, so much — listen —
I am the Self, the inner Self, O Guḍākeśa; 'guḍākā' is sleep, of that the master is 'īśa' — hence 'Guḍākeśa,' one who has conquered sleep; this is the meaning; or, alternatively, 'thick-haired.' Situated in the abode of all beings — in the abode, in the heart within, of all beings, situated — I, the Self, the inner Self, am always to be meditated upon. But by one incapable of that, I am to be thought of in the topics that follow; because I alone am the beginning, the cause, of beings, and likewise the middle, the persistence, the end, the dissolution.
Gītā Vāhini
“అర్జునా! చాలా చిన్న కోరికనే కోరితివి. ఇది నీకంత సులభముగా అర్థమగుననుకొంటివా? అడిగితివి కనుక దయతో తెలుపుదును, విను. సకల భూతముల యొక్క హృదయ కమలములందుండు ‘ప్రత్యగాత్మ’ను నేనే. దీనినే ‘ఆత్మ’ అని అందురు. దానిని ధ్యానించిన చాలును. అనగా ‘సర్వభూతముల యొక్క ప్రత్యగాత్మ’ అని విశ్వసించిన చాలును, అదే ధ్యానము. ఇట్టి విశ్వాసమునకు, ప్రతిబంధకములు కలుగక దృధవ్రతుడై ఆచరణల యందు నిరూపణ సలిపినపుడు ‘నీవే నేను, నేనే నీవు’గా అనుభవింతువు. అనగా, ఏకత్వము పొందవచ్చును.”
In plain words
“Arjuna! What a very small wish you have made! Did you think this would be so easy for you to understand? Since you have asked, I shall tell you out of compassion; listen. I am the ‘Pratyagātma’ dwelling in the heart-lotus of every being. This is what is called the ‘Ātma’. It is enough to meditate on that. That is, it is enough to believe that I am ‘the Pratyagātma of all beings’; that itself is dhyāna. When you hold to this faith, letting no obstacle arise to it, firm in your vow, and prove it in your practice, you will experience ‘You are I, I am you’. That is, oneness can be attained.”