In plain words
Some yogins perform yajña to the devas alone; others offer the self as yajña, by the self itself, into the fire of Brahman.
Word for word
Some yogins perform yajña to the gods alone; others offer yajña [the self] by yajña [the self] itself in the fire of brahman.
The commentators
Bhagavadgītābhāṣyam
तत्र अधुना सम्यग्दर्शनस्य यज्ञत्वं सम्पाद्य तत्स्तुत्यर्थम् अन्येऽपि यज्ञा उपक्षिप्यन्ते —
दैवमेव देवा इज्यन्ते येन यज्ञेन असौ दैवो यज्ञः तमेव अपरे यज्ञं योगिनः कर्मिणः पर्युपासते कुर्वन्तीत्यर्थः । ब्रह्माग्नौ ‘सत्यं ज्ञानमनन्तं ब्रह्म’(तै. उ. २ । १ । १) ‘विज्ञानमानन्दं ब्रह्म’ ‘यत् साक्षादपरोक्षात् ब्रह्म य आत्मा सर्वान्तरः’(बृ. उ. ३ । ४ । १) इत्यादिवचनोक्तम् अशनायादिसर्वसंसारधर्मवर्जितम् ‘नेति नेति’(बृ. उ. ४ । ४ । २२) इति निरस्ताशेषविशेषं ब्रह्मशब्देन उच्यते । ब्रह्म च तत् अग्निश्च सः होमाधिकरणत्वविवक्षया ब्रह्माग्निः । तस्मिन् ब्रह्माग्नौ अपरे अन्ये ब्रह्मविदः यज्ञम् — यज्ञशब्दवाच्य आत्मा, आत्मनामसु यज्ञशब्दस्य पाठात् — तम् आत्मानं यज्ञं परमार्थतः परमेव ब्रह्म सन्तं बुद्ध्याद्युपाधिसंयुक्तम् अध्यस्तसर्वोपाधिधर्मकम् आहुतिरूपं यज्ञेनैव आत्मनैव उक्तलक्षणेन उपजुह्वति प्रक्षिपन्ति, सोपाधिकस्य आत्मनः निरुपाधिकेन परब्रह्मस्वरूपेणैव यद्दर्शनं स तस्मिन् होमः तं कुर्वन्ति ब्रह्मात्मैकत्वदर्शननिष्ठाः संन्यासिनः इत्यर्थः ॥ २५ ॥
In plain words
Now, having shown that right vision is itself a sacrifice, other sacrifices are brought in as well, in order to praise it —
'To the deity alone' — the gods are the ones being worshipped; whatever sacrifice honors a deity is a deity-sacrifice, and that is what some — the yogins, the ritual performers — offer, meaning they carry it out. 'In the fire of Brahman': Brahman is what scripture describes as 'truth, knowledge, the infinite' (Tai. Up. 2.1.1), 'consciousness, bliss', 'that which is immediate and direct, the Self within everyone' (Bṛh. Up. 3.4.1) — free of hunger and every other trait of worldly existence, its every particular feature stripped away by 'not this, not this' (Bṛh. Up. 4.4.22). That is what the word 'Brahman' means here. What is Brahman and what is fire, taken together as the receptacle for the offering, is called 'the fire of Brahman'. Into that fire, other knowers of Brahman offer the sacrifice — and here 'sacrifice' means the Self itself, since the word 'sacrifice' is actually listed among the Self's own names. That Self — which is, in truth, nothing but the supreme Brahman, though wrapped in the intellect and other limiting adjuncts and carrying, as if its own, every property of those superimposed adjuncts, cast here in the shape of an offering — that very Self is what they pour, by means of that very Self, into the fire. What this really means is: the vision of the conditioned Self purely as the unconditioned nature of supreme Brahman — that vision itself is the offering, and that is what these renunciates, established in the vision that Brahman and the Self are one, are pouring into that fire. That is the meaning.
Close to the Sanskrit
There, now, having established the sacrifice-hood of right vision, for the purpose of its praise, other sacrifices too are brought in —
'To the deity alone' — the gods are the ones worshipped; by whichever sacrifice that is the deity-sacrifice — that very sacrifice some, the yogins, the ritual performers, offer — meaning they perform it. 'In the fire of Brahman' — [Brahman is] what is spoken of by such texts as 'truth, knowledge, infinite — Brahman' (Tai. Up. 2.1.1), 'consciousness, bliss — Brahman', 'that which is direct, immediate, Brahman, the Self within all' (Bṛh. Up. 3.4.1), devoid of every worldly property beginning with hunger, whose every particularity has been negated by 'not this, not this' (Bṛh. Up. 4.4.22) — that is denoted by the word 'Brahman'. That which is Brahman and that which is fire — that, meant as the receptacle of the offering, is 'the fire of Brahman'. In that fire of Brahman, other knowers of Brahman offer the sacrifice — 'sacrifice' here denotes the Self, since the word 'sacrifice' is listed among the names of the Self — that Self, the sacrifice, which in the highest sense is the supreme Brahman itself, but which, joined to limiting adjuncts such as the intellect, carries as its own property every superimposed adjunct, in the form of an oblation — by that very sacrifice, that is, by the Self itself, of the character just described, they pour it in, cast it in — that is: the vision of the conditioned Self purely as the unconditioned nature of the supreme Brahman — that vision itself is the offering, and into that they perform it — the renunciates fixed in the vision that Brahman and the Self are one. This is the meaning.