1 Gita Sloka Every Day - Chapter 18 - Moksha Sanyasa Yoga - Sloka 7

The entire content of this mail is from Shri V N Gopala Desikan's  Srimad Bhagavad Gita, published by Vishishtadvaita Research Centre, Chennai and The Bhagavad Gita by Swami Chidbhavananda published by Ramakrishna Mission

Tamasika and Rajasika tyagas are purposeless 7-8

1 Gita Sloka  Every Day - Chapter 18 - Moksha Sanyasa Yoga - Sloka 7

Krishna in Deavki's womb

Niyatsya tu sanyasah karmanah na upadyate I

Mohat tasya parityagah tamasah parikirtitah II sloka 7

नियतस्य तु सन्यासः कर्मणः न उपध्यते I 

मोहात् तस्य परित्यागः तामसः परिकीर्तितः II श्लोक 7

Verily the abandonment of any obligatory duty is not proper; such abandonment out of ignorance is declared to be tamasika.

A person should not give up the performance of compulsory duites, prescribed by shastras, in accordance with one's caste and ashrama (grihastha etc); which (duites) consist of nitya and naimittika karmas like pancha maha yagna. Otherwise, even the maintenac eof the body will not be possible, as stated in Chapter 3, sloka 8.

Maintaining the body, by eating the remains of the yagnas, produces correct knowledge. Eating food which is not of the remains of yagnas (pancha mahayagna) results in sin; and produces perverse knowledge (Chapter 3 sloka 13). Also the true knowledge of the Brahman is dependent on the purity of the  food. When the food is pure, the mind is pure. When the mind is pure, there arises loving meditation of the Lord; which results in liberation of the soul. 

Therefore, the pancha mahayagna and such compulsory karmas should be done till death. After performing such yagnas, the remains should be eaten; which will produce the true knowledge of Brahman. So, giving up these compulsory karmas is not proper.

Giving up such karmas, due to delusion that doing such karmas will result in the bondage of samsara is declared as tamasa tyaga. It arises due to perverse knowledge.