In plain words
One who performs actions, offering them to Brahman and abandoning attachment, is untouched by sin, like a lotus leaf by water.
Word for word
Who acts, placing actions in Brahman and having abandoned attachment, he is not tainted by sin, as a lotus leaf [is not] by water.
The commentators
Bhagavadgītābhāṣyam
यस्तु पुनः अतत्त्ववित् प्रवृत्तश्च कर्मयोगे —
ब्रह्मणि ईश्वरे आधाय निक्षिप्य ‘तदर्थं कर्म करोमि’ इति भृत्य इव स्वाम्यर्थं सर्वाणि कर्माणि मोक्षेऽपि फले सङ्गं त्यक्त्वा करोति यः सर्वकर्माणि, लिप्यते न स पापेन न सम्बध्यते पद्मपत्रमिव अम्भसा उदकेन । केवलं सत्त्वशुद्धिमात्रमेव फलं तस्य कर्मणः स्यात् ॥ १० ॥
In plain words
But the other man — the one who has not seen the truth of things, and who has stepped into the discipline of action —
'In Brahman' means in the Lord. 'Having dedicated' his actions means having laid every one of them down there, thinking, 'I do this for him,' the way a servant acts for his master's sake, not his own. He performs every action having let go of attachment to any fruit — even to liberation itself as a fruit. Such a person isn't stained by sin, isn't caught by it, any more than a lotus leaf is caught by the water it sits on. The only thing that comes of such action is a purified inner being — nothing more.
Close to the Sanskrit
But he who, again, is not a knower of the truth and is engaged in the yoga of action —
'In Brahman' — in the Lord — 'having dedicated,' having laid down [all actions], thinking, 'I do this action for his sake,' like a servant [acting] for his master's sake — 'all actions,' having abandoned attachment even to liberation as the fruit, 'performs' — who performs all actions — 'is not tainted' by sin, is not bound, 'as a lotus leaf' by water. Merely the purity of the inner being alone would be the result of that action.