tatra sattvam nirmalatvaatprakaashamanaamayam |
sukhasangena badhnaati jnyaanasangena chaanagha || 6 ||

Of these, sattva is pure, bright and healthy. It binds through attachment to joy and attachment to knowledge, O sinless one.
tatra : of these
sattvam : satvva
nirmalatvaat : pure
prakaasham : bright
anaamayam : healthy
sukhasangena : attachment to joy
badhnaati : binds
jnyaanasangena : attachment to knowledge
cha : and
anagha : O sinless one
In simple terms, our mind is in a state of sattva whenever we experience joy, peace and calmness. We are alert, our mind is able to think very logically, we are able to grasp the most complex statements that we read or hear, and we don’t feel the need to rush out into the world.
Shri Krishna says that sattva refers to purity, brightness and health. Our mind can be compared to the water in a glass cup. When the pond is free from agitation, and all the dirt has settled down, it is crystal clear and is able to reflect light beautifully. Similarly, when our mind is in a state of sattva, there is absence of dirt in the form of selfish desires. There is brightness because it is able to reflect the light of the self, the awareness of the self, without any hinderance. There is health because it enables us to get as close to our natural state of joy as is possible in the human body.
Now, no matter how enjoyable or pleasant this state is, Shri Krishna reminds us that sattva has the ability to bind us, to trap us, because anyone will like to remain in a state of joy and calmness. Furthermore, if we foresee that this state will go away, we would like to hold on to this state of joy tightly and not let it go. Sattva can also bind us through attachment to knowledge. Since sattva enables our mind to accumulate more and more worldly knowledge, read more books, attain more academic qualifications, and ultimately pump up our ego, we get attached to it even more.
Why is sattva able to bind us to joy and knowledge? We mistake the joy provided by sattva because we have not experienced what real joy is. That can only happen in meditation when we are able to access the joy that is inherent in the “I”, in the self. All other joys are in the realm of Prakriti – temporary, perishable, and illusory. True joy is in the subject, the “I”, not in the object. Sattva, though preferable to rajas and tamas, is to be used for getting us closer to the goal of liberation, and has to be ultimately discarded, just like the fire is turned off after we cook our meal.