vidhiheenamasrishtaannam mantraheenamadakshinam |
shraddhaavirahitam yajnyam taamasam parichakshate || 13 ||

They call that sacrifice to be taamasic which is contrary to scripture, in which no food is distributed, without chanting of hymns or donations to priests, and performed without faith.
vidhiheenam : contrary to scripture
asrishtaannam : without distribution of food
mantraheenam : without chanting of hymns
adakshinam : without donation to priests
shraddhaavirahitam : performed without faith
yajnyam : sacrifice
taamasam : taamasic
parichakshate : they call
Here, Shri Krishna describes the attitude of taamasic individuals towards action, using the symbolism of a sacrificial ritual once again. He says that taamasic attitude towards action totally disregards shaastra or scripture. Scripture refers to a higher law, any notion of ethics or morality. There is no thought as to the consequence of the action to oneself and to other individuals whatsoever. Any task done without proper planning or performed haphazardly falls into this category.
Next, Shri Krishna says that there is no distribution of food in the sacrifice. In the taamasic attitude, the person not only claims the results of the action as their own, but goes to great lengths to ensure that no one else gains the benefit of the action, even if it is their due. For instance, if a business has a good year, the owner may hoard the profits instead of giving employees a bonus. Furthermore, the taamasic attitude does give respect or listen to advice of senior people, referred to as “priests” in this shloka.
The main problem with the taamasic attitude is that all actions are performed with lack of faith. In other words, actions are performed for all the wrong reasons – someone else told us to perform the action, we are just doing it for the sake of doing it, we are doing it grudgingly, we are not putting our heart into it, we are not involved in it and so on. The performance of actions is as if it is being done by a lifeless entity, a corpse.