Based on three qualities (Rajogun, Tamogun & Satogun) even food, Yagya and Sacred activities also differ. Seventeeth chapter emphasises to do every action with pure faith and reverance.

(The Yoga of Three-Fold Faith)

The Bhagvad Gita is an extraordinary scripture which touches every aspect for self-evolution in life and also makes it an inspiration. It also warns against the probable obstacles which may be encountered. After relating the evil consequence of abandoning the scriptural laws, in the conclusion of the 16th chapter, inspiration has been provided to make the scripture as an ideal of life. Both aspects have been discussed - giving up the scriptural norms and then accepting the scriptural rules and moving forward in the journey of life. Warning has also been given and inspiration provided too! Why should the scriptures be considered as an authority? Its need also has been clarified. The distinction between what ought to be done and what ought not to be done will only become clear on accepting the scripture as the ideal. Here one more doubt can arise in the mind when this is practiced! Arjun as the representative of mankind raises this very doubt in the form of an enquiry with Lord Shri Krishna.