Bhagavad Gita Verse 37, Chapter 4

yathaidhaamsi samiddhognirbhasmasaatkuruterjuna |
jnyaanaagnihi sarvakarmaani bhasmasaatkurute tathaa || 37 ||
 
Just as a burning flame turns fuel into ashes, O Arjuna, so does the fire of knowledge turn all actions into ashes.
 
yathaa : just as
edhaamsi : fuel
samiddhaha : burning
agnihi : flame
bhasmasaat : ashes
kurute : turn into
arjuna : O Arjuna
jnyaana-agnihi : fire of knowledge
sarvakarmaani : all actions
bhasmasaat : ashes
kurute : turn into
tathaa : so does
 
Previously, Shri Krishna mentioned that having gained knowledge, we will be able to cross over all our sins. But does that mean that the sins remain hidden somewhere? In this shloka, he says that all sins or karmaas get destroyed with knowledge. Just as fire has the capability to burn fuel in the form of wood or coal into ashes, so does knowledge totally destroy karmaas.
 
Karmaas accumulate in our psyche due to ignorance of our true identity. Now, knowledge and ignorance are mutually exclusive. One cannot remain when the other is present. Take an example from early school. Once you what the addition symbol "+" does, you no longer get confused when you see a question on addition.
 
So when knowledge comes, ignorance is destroyed, as well as karmaas that were created a result of ignorance. And when the sense of doership and enjoyership vanishes, then situations do not cause joy or sorrow. No more karmaas are accumulated.
 
In this manner, Shri Krishna continues to praise knowledge in this shloka and the following two shlokas.

Bhagavad Gita Verse 21, Chapter 3

yadyadaacharati shreshthastattadevetaro janaha |
sa yatpramaanam kurute lokastadanuvartate || 21 ||
 
Whatever an ideal person does, so do other people (imitate him). Whatever standard he sets, other people follow.
 
yat yat  : just as
aacharati : a person does
shreshthaha : ideal
tat tat : in that manner
eva : only
itarah : other
janaha : people
sah : he
yat : whatever
pramaanam : standard
kurute : does
lokah : other people
tat : like him
anuvartate : they behave
 
In the previous verse, Shri Krishna provided the example of king Janaka who, though being a warrior king, achieved self-realization through performance of karma yoga. Here Shri Krishna puts forth yet another argument to Arjuna, knowing very well that Arjuna always put others first before himself. Shri Krishna said that whosoever looked up to Arjuna as a role model would also take to this path if Arjuna followed it.
 
Now, an extremely important but subtle point made by Shri Krishna is hidden in the phrase "ideal person does". He wants us to realize that actions speak louder than words. For instance, we cannot expect our children to not drink alcohol or smoke if we preach to them, but drink and smoke ourselves. Not just children, but most people watch what we do and not what we say. Therefore, Shri Krishna urges us to practice karmayoga, and not to simply tell people that we are learning it and so on.
 
So in addition to urging us and Arjuna to perform karmayoga, Shri Krishna also reveals an important leadership lesson. The best way to lead is to lead by example, and not by making flowery speeches or hiring motivational speakers. This point is not just echoed in the management texts of today, but also in spiritual masterpieces such as the Dasbodh by Samarth Ramdas Swami.