Krishna uses a sharp word here: stena, a thief. The person who takes from the world — food, air, water, the labor of others — and gives nothing back is no different from someone who steals. The universe gave generously. To only consume and never contribute is to break the fundamental contract of existence.
This is not about ritual obligations alone. It is a principle for everyday life. The air you breathe, the food on your plate, the road you walk on — all of it came from somewhere, from someone's effort or nature's bounty. To live only for yourself, taking without giving, is what the Gita calls theft.