In plain words
It is the light even of all lights and is said to be beyond darkness. Jñāna, the object of jñāna, and that which is reached through jñāna abide in the heart of everyone.
Word for word
Of lights even, that is the light; it is said [to be] beyond darkness; knowledge, the knowable, what is reached by knowledge: [these are] seated in the heart of all.
ज्योतिषामपि तज्ज्योतिस्तमसः परमुच्यतेज्ञानं ज्ञेयं ज्ञानगम्यं हृदि सर्वस्य विष्ठितम्
Other commentaries
The commentators
▸Bhagavadgītābhāṣyam
किञ्च, सर्वत्र विद्यमानमपि सत् न उपलभ्यते चेत् , ज्ञेयं तमः तर्हि ? न । किं तर्हि ? —
ज्योतिषाम् आदित्यादीनामपि तत् ज्ञेयं ज्योतिः । आत्मचैतन्यज्योतिषा इद्धानि हि आदित्यादीनि ज्योतींषि दीप्यन्ते, ‘येन सूर्यस्तपति तेजसेद्धः’(तै. ब्रा. ३ । १२ । ९) ‘तस्य भासा सर्वमिदं विभाति’(मु. उ. २ । २ । ११) इत्यादिश्रुतिभ्यः ; स्मृतेश्च इहैव — ‘यदादित्यगतं तेजः’(भ. गी. १५ । १२) इत्यादेः । तमसः अज्ञानात् परम् अस्पृष्टम् उच्यते । ज्ञानादेः दुःसम्पादनबुद्ध्या प्राप्तावसादस्य उत्तम्भनार्थमाह — ज्ञानम् अमानित्वादि ; ज्ञेयम् ‘ज्ञेयं यत् तत् प्रवक्ष्यामि’(भ. गी. १३ । १२) इत्यादिना उक्तम् ; ज्ञानगम्यम् ज्ञेयमेव ज्ञातं सत् ज्ञानफलमिति ज्ञानगम्यमुच्यते ; ज्ञायमानं तु ज्ञेयम् । तत् एतत् त्रयमपि हृदि बुद्धौ सर्वस्य प्राणिजातस्य विष्ठितं विशेषेण स्थितम् । तत्रैव हि त्रयं विभाव्यते ॥ १७ ॥
In plain words
And here is another point: if something exists everywhere and yet is not perceived — does that make the object of knowledge simply darkness? No, not that. Then what is it? —
Even of the great luminaries — the sun and everything like it — that same reality is their light. Because the sun and its kin only blaze at all because they have been kindled by the light of the Self's own consciousness. Scripture tells us this again and again: 'By whom the sun, kindled by his radiance, gives its heat' (Taittirīya Brāhmaṇa 3.12.9); 'By his light, all of this shines' (Muṇḍaka Upaniṣad 2.2.11). And this very text says the same, right here: 'Whatever light belongs to the sun...' (Bhagavad Gītā 15.12). It is called beyond darkness — utterly untouched by ignorance. Now, because someone might sink into despair thinking knowledge is just too hard to reach, Kṛṣṇa steps in to strengthen their resolve, laying it all out clearly: 'knowledge' is humility and everything alongside it; 'the object of knowledge' is exactly what was already declared in the verse beginning 'That which is to be known, I shall declare' (Bhagavad Gītā 13.12); and 'attainable through knowledge' means this — once the object of knowledge is actually known, once it has become the fruit of that knowing, that is what we call 'reached through knowledge.' But the very process of coming to know it — that, while it is happening, is simply called the object of knowledge itself. All three of these live together in the heart, in the intellect, of every single living being — that is exactly where they are found. It is there, and only there, that all three actually reveal themselves.
Close to the Sanskrit
Moreover, if [something], though existing everywhere, is not perceived — is the object of knowledge, then, darkness? No. Then what [is it]? —
Even of the luminaries — the sun and so on — that [is] the light [of them, i.e. the object of knowledge is their light]. For, kindled by the light of the Self's own consciousness, the sun and so on, [these] luminaries, shine — from scriptural statements beginning with 'by whom the sun, kindled by [his] radiance, gives heat' (Taittirīya Brāhmaṇa 3.12.9) [and] 'by his light all this shines' (Muṇḍaka Upaniṣad 2.2.11); and from smṛti, right here [in this very text] — [namely, the verse] beginning 'whatever light belongs to the sun' (Bhagavad Gītā 15.12). It is called beyond darkness, [that is] untouched by ignorance. With the intention of propping up [the resolve of] one who has fallen into despondency from the thought that knowledge and so on is hard to accomplish, [Kṛṣṇa] says — 'knowledge' [is] humility and so on; 'the object of knowledge' [is what] has been stated by [the verse] beginning 'that which is to be known, I shall declare' (Bhagavad Gītā 13.12) and so on; 'attainable through knowledge' [is] this: the very object of knowledge, when known, being the fruit of knowledge, is called 'attainable through knowledge'; whereas 'being known' [itself] is [called] the object of knowledge. All these three, indeed, abide, situated specifically, in the heart, [that is] in the intellect, of every born creature — [they are] established there. For it is precisely there that the three are discerned.