Bhagavad Gita Verse 29, Chapter 3

prakritergunasammoodhaah sajjante gunakarmasu |
taanakritsnavido mandaankritsnavinna vichaalayet || 29 ||
 
People deluded by the gunaas of prakriti are attached to gunaas and action. The wise person does not disturb those fools who are of limited knowledge.
 
prakriteh : from prakriti
guna-sammoodhaah : people deluded by the gunas
sajjante : are attached to
guna-karmasu : gunas and karmas
taan : those
akritsna : limited
vidah : knowledge
mandaan : fools
kritsna : complete
vit : one who knows
vichaalayet : do not disturb
 
Shri Krishna uses this shloka to reiterate the difference between a wise person and an ignorant or foolish person. It is nothing but their degree of attachment to gunaas (forces of nature) and their actions. He also restates that wise people should not preach karmayoga to those who are attached to gunaas and their actions. Instead, they should lead by example.
 
Why should they do so? The teacher in a school does not condemn or ridicule a student's ignorance about mathematics. He fully well knows that the student is in very early stages of his curriculum. With enough time and practice, the student will evolve into a higher level of math understanding.
 
Similarly, a wise person does not condemn or judge anyone, knowing that everyone is at a different level of spiritual evolution. “Judge not, that ye be not judged” as the Bible says in Matthew 7.1.
 
As a point of clarification, let us reexamine the message of the last 2 shlokas, which was that most of us mistakenly think that the "I" is the doer. We had seen that it is a tough statement to swallow, so let's look at a common question that arises when one hears this statement. "I am a well renowned surgeon. I just completed a successful triple-bypass surgery. So if I did not do it, who did?"
 
There was a team of three "agents" that performed the operation - the surgeon's mind, body and intellect. The mind gathered data from the five senses and presented it to the intellect. The intellect, based on past experiences and knowledge, took decisions. These decisions were sent to the surgeon's body, specifically the fingers, which performed the operation.
 
The real "I", which is the eternal essence, was a witness of this entire surgery. But the principle of the ego or ahamkaara created a mix-up between the real-I and the three agents: mind, body and intellect. Reversing this fundamental mix-up is the ultimate goal of karmayoga, in fact, of any yoga.