As per i listen from some people, is it written in Bhagavat Gita? that
If someone don't offer anything to god before he starts his daily activities then that person is considered as a thief.
Yes, here is what Krishna says in chapter 3 of the Bhagavad Gita:
The demigods, being pleased by sacriﬁces, will also please you, and thus, by cooperation between men and demigods, prosperity will reign for all. In charge of the various necessities of life, the demigods, being satisﬁed by the performance of yajña [sacriﬁce], will supply all necessities to you. But he who enjoys such gifts without offering them to the demigods in return is certainly a thief. The devotees of the Lord are released from all kinds of sins because they eat food which is offered ﬁrst for sacriﬁce. Others, who prepare food for personal sense enjoyment, verily eat only sin.
Here is what Adi Shankaracharya says about the thief line:
Sah, he; is eva, certainly; a stenah, thief, a stealer of the wealth of gods and others; yah, who; bhunkte, enjoys, gratifies only his own body and organs; with dattan, what enjoyable things have been given; taih, by them, by the gods; apradaya, without offering (these); ebhyah, to them, i.e. without repaying the debt [The three kinds of debt-to the gods, to the rsis (sage), and to the manes-are repaid by satisfying them through sacrifices, celibacy (including study of the Vedas, etc.), and procreation, respectively. Unless one repays these debts, he incurs sin.] to them.’
And here is what Ramanujacharya says:
Whoever enjoys the objects of enjoyment granted by them for the purpose of worshipping them, without giving them their due share in return — he is verily a thief. What is called ‘theft’ is indeed taking what belongs to another as one’s own and using it for oneself, when it is really designed for the purpose of another.
In any case, the debt alluded to is the one described in this chapter of the Taittiriya Samhita of the Yajur Veda:
A Brahman on birth is born with a threefold debt, of pupilship to the Rsis, of sacrifice to the gods, of offspring to the Pitrs. He is freed from his debt who has a son, is a sacrificer, and who has lived as a pupil
The verse is an ancient form of what we refer today as "conservativism".
BG 3.12 - Being nourished by sacrifices, the gods will indeed give you the coveted enjoyments. One is certainly a thief who enjoys what have been given by them without offering [these] to them.'
The verse refers to those, who even after gaining privileges from society or nature, don't follow their duty to pay back by observing responsibility. It happens either due to greed (born out of Rajas / passion) or laziness (born out of Tamas / ignorance).
In ancient time, every aspect of nature was considered as deva. E.g. the one who brings water is called Varuna deva. One becomes a thief, when one doesn't support the cycle of rain or water, either by cutting too many trees without planting, waste water without conserving, polluting rivers irreversibly ...
Similarly there is aunified deva for animals as Pashupati, for fire it is Agni, for air it is VAyu, for society it's king & so on.