Bhagavad Gita Verse 3, Chapter 17

sattvaanuroopaa sarvasya shraddhaa bhavati bhaarata |
shraddhaamayoyam purusho yo yacchraddhaha sa eva saha || 3 ||
 
The faith of each is according to his nature, O Bhaarata. This human being is comprised of faith. As his faith, so is he.
 
sattvaanuroopaa : according to nature
sarvasya : of each
shraddhaa : faith
bhavati : is
bhaarata : O Bhaarata
shraddhaamayaha : comprised of faith
ayam : this
purushaha : human being
yaha : he who
yacchraddhaha : as his faith
saha : so
eva : only
saha : he
 
Shri Krishna emphasized the point made in the earlier shloka. The human being is nothing but a bundle of faiths, also known as beliefs, prejudices, customs, culture, tradition, basically everything that is ingrained into us as samskaaraas or impressions. But where do these impressions come from? Some of these impressions come from external factors, and some of these are present in us right from our birth.
 
When we see a child prodigy perform a complicated symphony, we may say that she got this skill from non stop practice since her birth, or we may say that she got it from her practice in a previous life. In any case, her actions are a product of the samskaaraas or impressions formed through countless hours of practice.
 
Shri Krishna says that faith is according to one’s sattva. Here, sattva is not used in its traditional meaning as a guna like rajas and tamas. Sattva refers to our svaabhaava, our nature, the bundle of impressions that are stored in our inner instrument, our antaha karana, which is comprised of our mind, intellect, memory and senses. This sattva, this bundle of impressions, makes us choose our actions throughout our lives. Although we think of ourselves as rational individuals, we use logic and reason to justify and rationalize our faith, in a roundabout way.
 
Now we come back to the question posed in the previous shloka. How can we assess the texture of our faith, our beliefs and our prejudices? We need to examine our actions. Our faith, our beliefs and our prejudices guide our actions. Therefore, by examining the texture of our actions, we can determine the texture of our faith. Our faith could be saatvic, raajasic or taamasic. Shri Krishna now takes each aspect of our actions and gives us guidelines on how to determine their texture.