Bhagavad Gita Verse 30, Chapter 18

pravrittim cha nivrittim cha kaaryaakaarye bhayaabhaye |
bandham moksham cha yaa vetti buddhihi saa paartha saattvikee || 30 ||
 
That intellect which knows engagement and withdrawal, what is duty and what is not, fear and fearlessness, bondage and liberation, O Paartha, that is saattvic.
 
pravrittim : engagement
cha : and
nivrittim : withdrawal
cha : and
kaaryaakaarye : what is duty and what is not
bhayaabhaye : fear and fearlessness
bandham : bondage
moksham : liberation
cha : and
yaa : which
vetti : knows
buddhihi : intellect
saa : that
paartha : O Paartha
saattvikee : is saattvic
 
Our jnyaanam, our knowledge, gives us an object to pursue, person to approach, or situation to create. Now it is upto our buddhi, our intellect, to decide the course of action. Typically, for any objectve, we need to decide whether or not we want pursue the objective, and if we do, how should we go about doing it. Shri Krishna says that a saattvic intellect, a saattvic buddhi is one that is clear on those two factors. In fact, Shri Krishna breaks the two factors down into four assessments: assessing one's stage in life and one's svadharma first, then whether an action is one's duty or not, then whether to be fearful or not, and lastly, whether to continue to act or not.
 
As we will see in a later topic in this chapter, the varna aashrama system, the system of aptitude and stage of life, helps us determine whether we should act at all, and if so, which actions should we perform and which we should not. A student should focus on studying, not in creating a family. A soldier should focus on protecting his country, not making money by selling his country out. The varna aashrama system helps address the first two assessments: engagement and withdrawal, and what is our duty and what is not. For example, if we get a new business proposal, we should assess whether we have the aptitude to execute it, but also, whether we are in the right stage of life. It is no use starting a new business when we are in our late sixties.
 
Once the varna aashrama system has approved the performance of an action, we need to test whether the action is motivated by personal reward, or whether it is motivated by selfless service. If we have fear in our mind while performing an action, chances are that a trace of egoism has crept into it. We may be doing the action out of the need for praise and honour. But if our mind is fearless, we can assume that our action is motivated out of selflessness. Lastly, as we perform one action after another, we should always examine whether these actions are taking us closer to liberation, or are further entrenching us in the material world. An intellect that guides us in such a manner is termed saattvic.