In plain words
Jñāna, action, and the agent are each said in the enumeration of guṇas to be threefold only, according to the distinction of guṇas. Hear these too, properly described.
Word for word
Knowledge and action and the agent are declared threefold only, by the difference of the guṇas, in the enumeration of the guṇas; hear them too as they are.
ज्ञानं कर्म च कर्ता च त्रिधैव गुणभेदतःप्रोच्यते गुणसङ्ख्याने यथावच्छृणु तान्यपि
Other commentaries
The commentators
▸Bhagavadgītābhāṣyam
अथ इदानीं क्रियाकारकफलानां सर्वेषां गुणात्मकत्वात् सत्त्वरजस्तमोगुणभेदतः त्रिविधः भेदः वक्तव्य इति आरभ्यते —
ज्ञानं कर्म च, कर्म क्रिया, न कारकं पारिभाषिकम् ईप्सिततमं कर्म, कर्ता च निर्वर्तकः क्रियाणां त्रिधा एव, अवधारणं गुणव्यतिरिक्तजात्यन्तराभावप्रदर्शनार्थं गुणभेदतः सत्त्वादिभेदेन इत्यर्थः । प्रोच्यते कथ्यते गुणसङ्ख्याने कापिले शास्त्रे तदपि गुणसङ्ख्यानशास्त्रं गुणभोक्तृविषये प्रमाणमेव । परमार्थब्रह्मैकत्वविषये यद्यपि विरुध्यते, तथापि ते हि कापिलाः गुणगौणव्यापारनिरूपणे अभियुक्ताः इति तच्छास्त्रमपि वक्ष्यमाणार्थस्तुत्यर्थत्वेन उपादीयते इति न विरोधः । यथावत् यथान्यायं यथाशास्त्रं शृणु तान्यपि ज्ञानादीनि तद्भेदजातानि गुणभेदकृतानि शृणु, वक्ष्यमाणे अर्थे मनःसमाधिं कुरु इत्यर्थः ॥ १९ ॥
In plain words
Now, here, a threefold division has to be set out: action, everything that carries action out, and the fruit that follows are all made of the guṇas, so each divides three ways along the lines of sattva, rajas and tamas. With that, what follows begins.
'Knowledge' here functions grammatically as 'the object'. And 'karma' means simply activity — not the technical grammatical sense, the thing most desired — that too is called 'karma'. 'The agent' is the one who brings actions about. All three — knowledge, action, agent — are classified threefold, and the word 'indeed' rules out any category beyond the three guṇas; the whole division rests purely on the distinction between sattva and the other two. This same threefold analysis is also found in the Kāpila school's teaching on enumerating the guṇas — and that scripture really is authoritative on the topic of the guṇas and their experiencer. It's true that on the question of Brahman's absolute oneness it actually conflicts with our view; even so, those Kāpila teachers really are experts when it comes to analyzing how the guṇas function, primary and secondary. So that scripture too gets drawn on here, simply to lend support to the point about to be made — and that is no contradiction at all. 'Properly, by right reasoning, according to scripture — hear!' means: hear also these further distinctions of knowledge and the rest, all arising from this same division of the guṇas — and bring your mind to full concentration on the topic about to be taught.
Close to the Sanskrit
Now, at this point, since all of action, the factors of action, and their fruits are of the nature of the guṇas, a threefold division, according to the distinction of the guṇas sattva, rajas and tamas, is to be stated — thus is this begun.
'Knowledge' is 'the object' grammatically; the term 'karma' also means activity, not the technical grammatical factor, the most-desired object — that is 'karma'; and 'the agent' is the accomplisher of actions — threefold indeed; the restrictive particle is for the purpose of showing the absence of any category other than the guṇas, by the distinction of the guṇas, by the distinction beginning with sattva — this is the meaning. It is declared, stated, in the enumeration of the guṇas, in the Kāpila scripture — that too, the scripture on the enumeration of the guṇas, is indeed authoritative on the topic of the guṇas and the experiencer. Although, on the topic of the oneness of the ultimate Brahman, it is contradicted, nevertheless they, the Kāpilas, are indeed skilled in the analysis of the guṇas' primary and secondary functions; thus, that scripture too is adopted by virtue of having the purpose of praising the point about to be made — thus, there is no contradiction. 'Properly', 'according to right reasoning', 'according to scripture' — 'hear!' — those too, knowledge and the rest, arisen as distinctions of that, made by the distinction of the guṇas — hear! — in the topic about to be stated, make concentration of mind — this is the meaning.