In plain words
Those deluded by the guṇas of Prakṛti become attached to the actions of the guṇas. The one who knows the whole should not disturb those of limited understanding.
Word for word
Those deluded by the guṇas of prakṛti are attached to the actions of the guṇas; the knower of the whole should not unsettle those dull ones who do not know the whole.
The commentators
Bhagavadgītābhāṣyam
ये पुनः —
प्रकृतेः गुणैः सम्यक् मूढाः संमोहिताः सन्तः सज्जन्ते गुणानां कर्मसु गुणकर्मसु ‘वयं कर्म कुर्मः फलाय’ इति | तान् कर्मसङ्गिनः अकृत्स्नविदः कर्मफलमात्रदर्शिनः मन्दान् मन्दप्रज्ञान् कृत्स्नवित् आत्मवित् स्वयं न विचालयेत् बुद्धिभेदकरणमेव चालनं तत् न कुर्यात् इत्यर्थः ॥ २९ ॥
In plain words
Those, on the other hand, who —
Nature's guṇas have them completely fooled, and in that fog they cling to the works the guṇas drive, telling themselves, "We are doing this, and we are doing it for what it pays." They are attached to action. They do not know the whole — meaning they see the fruit and nothing else. They are dull, dull in their power to discern. And the one who does know the whole, who knows the Self, is not to unsettle them. Unsettling them means exactly this: splitting open the conviction they are working from. That is what he must not do.
Close to the Sanskrit
But those who —
Thoroughly deluded — bewildered — by the guṇas of prakṛti, they cling to the actions of the guṇas, that is, to guṇa-karmas, thinking, 'we perform action for its fruit.' Those attached to action, not knowers of the whole — that is, seeing nothing but the fruit of action — dull, that is, dull in understanding: the knower of the whole, the knower of the Self, should not himself unsettle them. The causing of a split in their understanding is precisely that unsettling; that he should not do. Such is the meaning.