Bhagavad Gita Chapter 03, Text 28

Bg 3.28

tattva-vit tu maha-baho
guna gunesu vartanta
iti matva na sajjate

Word for word: 
tattva-vit — the knower of the Absolute Truth; tu — but; maha-baho — O mighty-armed one; guna-karma — of works under material influence; vibhagayoh — differences; gunah — senses; gunesu — in sense gratification; vartante — are being engaged; iti — thus; matva — thinking; na — never; sajjate — becomes attached.

Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
One who is in knowledge of the Absolute Truth, O mighty-armed, does not engage himself in the senses and sense gratification, knowing well the differences between work in devotion and work for fruitive results.

Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The knower of the Absolute Truth is convinced of his awkward position in material association. He knows that he is part and parcel of the Supreme Personality of Godhead, Krishna, and that his position should not be in the material creation. He knows his real identity as part and parcel of the Supreme, who is eternal bliss and knowledge, and he realizes that somehow or other he is entrapped in the material conception of life. In his pure state of existence he is meant to dovetail his activities in devotional service to the Supreme Personality of Godhead, Krishna. He therefore engages himself in the activities of Krishna consciousness and becomes naturally unattached to the activities of the material senses, which are all circumstantial and temporary. He knows that his material condition of life is under the supreme control of the Lord; consequently he is not disturbed by all kinds of material reactions, which he considers to be the mercy of the Lord. According to Srimad-Bhagavatam, one who knows the Absolute Truth in three different features – namely Brahman, Paramatma and the Supreme Personality of Godhead – is called tattva-vit, for he knows also his own factual position in relationship with the Supreme.