Bhagavad Gita Verse 11, Chapter 14

sarvasvaareshu dehesminprakaasha upajaayate |
jnyaanam yadaa tadaa vidyaadvivriddham sattvamityuta || 11 ||
 
When luminous knowledge radiates through all gates of this body, then one should know that sattva has increased greatly.
 
sarvasvaareshu : in all gates
dehe : body
asmin : this
prakaashaha : luminous
upajaayate : radiates
jnyaanam : knowledge
yadaa : when
tadaa : then
vidyaat : one should know
vivriddham : increased
sattvam : sattva
iti : this
uta : definitely
 
What are the marks of sattva? Shri Krishna says that when we see radiance, or when we see knowledge radiating from a person, we should know that we are in the presence of a highly sattvic person. The word “dvaara” usually means door or gate, but here it refers to the sense organs, our doors to the world. Even though the sense organs are meant from receiving stimuli from the world, they can also convey our internal state to the world. Our eyes, especially, can give away our thoughts. If our mind is wandering, our eyes will also wander, for instance. In a sattvic person, radiance shines through the sense organs, especially the eyes.
 
Now, we should not think that a highly sattvic person will radiate beams of light from their body. But they do radiate calmness and peace. We can sense peace if we are near them, or pick up on their calmness if we are watching them on a screen. Watch Dr. Jane Goodall speak about her efforts to save gorillas in Africa, and you will be drawn to the serenity on her face instantly. Such people harbour few, if any, selfish desires in their mind. This lack of dirt in the form of selfishness lets their inner radiance, the light of their eternal essence, shine through.
 
From our perspective, whenever we notice an increase in clear thinking, we should know that sattva is predominant in our mind. If we see fried food but the intellect prevents our hand from reaching to pick up that food, we are in a sattvic state. If our thoughts are towards the well-being of the family, our city or our nation, instead of just our narrow well-being, we are in a sattvic state. If our mind is sharp and alert, if we don’t let anything drop in our personal and professional lives, we are in a sattvic state.