Three qualities of our body and mind.

sattvam rajas tamas iti,gunah prakrtisambhavah,
nibadhnanti mahabaho,dehe dehinam avyayam.---5

Everybody is tied to a -mod as classified by their nature and effect as sattvic,rajas,tamas.--5
Three gunas[modes] are like this,sattvica,[goodness]Rajas[passion]Tamas[dullness] These mods lies in our body as a part of nature.they are according our previous lives.we can see some people are peaceful,claim by nature,they are from 'sattvic'nature.some are hard worker talkative nature worldly affairs are most important for him.They can not sit for a while.the are from rajas nature.but still there are from tamas nature they are of lazy nature.they do not work hard.they are extremely self centered.
These qualities are of our mind and body. because our body follows our mind.so Lord Krishana describes these three mods because after knowing them we can find the way to self realization.