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एव उपमानाद्यविषयत्वम् ।तथा न चक्षुषा पश्यति कश्चित् अपि एनं सर्वान्तरं परमात्मानम् ।कथं तर्हि पश्यन्ति? मनीषया अध्यवसायात्मिकया मनसा संकल्पविकल्पात्मकेन हृदा च हृदयेन च साधनभूतेन ।हृदयं विना नान्यत्र परमात्मन उपलब्धिः संभवतीति मत्वा हृदा चेत्युक्तम् ।अथवा, न केवलं मनोबुद्धिमात्रेण, अपि तु हृदा च हृदयस्थेन च परमेश्वरेणानुगृहीताः सन्तः ।य एनं परमात्मानं विदुः अयमहमस्मीति, ते अमृताः अमरणधर्माणो भवन्ति ।अथवा, हृदा हृदयेन परमात्मना ।तथा च हृत्स्थे परमात्मनि हृदयशब्दं निर्वक्ति—‘स एष आत्मा हृदि तस्यैतदेव निरुक्तं हृद्ययमिति तस्माद्धृद्यमिति अहरहर्वा एवंवित्स्वर्गं लोकमेति’ इति ।तथा च श्रुतिः तदधीनात्मसिद्धिं दर्शयति—‘यस्य देवे परा भक्तिर्यथा देवे तथा गुरौ ।तस्यैते कथिता ह्यर्थाः प्रकाशन्ते महात्मनः’ इति ।एवं यं विदित्वा अमृता भवन्ति, तं योगिन एव पश्यन्ति ॥
In plain words
...thus illustrating that He is beyond all comparisons. Similarly, no one perceives this innermost supreme Self with the physical eye. How then is He seen? Through a resolute intellect, a controlled mind, and through the purified heart acting as the instrument. Without the heart, realization of the supreme Self is impossible, which is why 'through the heart' is specified. Or rather, not merely through the mind and intellect, but by the heart graced by the Supreme Lord residing within it. Those who realize this supreme Self, knowing 'I am He,' become immortal and deathless. Alternatively, 'hṛdā' refers to the supreme Self itself as the heart. Thus the Śruti derives the word 'hṛdaya' with reference to the indwelling Atman: 'This Atman is in the heart. The explanation of it is this: it rests in the heart, therefore it is called hṛdyam. Day by day indeed such a knower enters the heavenly world.' And the Śruti shows that self-realization depends upon this: 'To that great-souled one who has supreme devotion to the Lord, and equal devotion to the guru, these declared truths shine forth brilliantly.' Thus, having known Him, the knowers become immortal; and yogis alone behold that Supreme Lord.
Close to the Sanskrit
...thus the condition of not being an object of comparison. Likewise, no one sees this innermost supreme Self with the eye. How then do they see? Through decisive intellect, mind of fluctuating thoughts, and through the heart and the heart as the instrument. Without the heart the attainment of the supreme Self is not possible, thus thinking 'through the heart' has been said. Or else, not solely by mind and intellect alone, but through the heart and through the Supreme Lord dwelling in the heart, being favored, whoever know this supreme Self as 'I am this', they become immortal, possessing deathless nature. Alternatively, 'hṛdā' means by the heart, the supreme Self. And thus the Śruti explains the word 'hṛdaya' regarding the supreme Self standing in the heart: 'This self is in the heart. Of this, this is the explanation: it is in the heart (hṛdyayam), therefore it is hṛdyam. Day by day indeed this knower attains the heavenly world.' And thus Śruti shows the self-accomplishment dependent upon that: 'Of whom there is supreme devotion to the deity, just as to the deity so to the guru, to that great-souled one these spoken meanings shine forth.' Thus, having known whom they become immortal, that Lord the yogis alone perceive.