One of the personal attendants came to the king and asked for leave of absence one year, to learn a mantra - Gayatri Mantra. The king thought that one year was too long and called him to come the next day. 

The king sent for a brahmin, got the Gayatri Mantra written down and committed it to memory ' in just thirty minutes. He asked the brahmin to check and confirm that his pronunciation and his delivery in terms of pauses and the duration of the sounds are correct. Then, the king could no longer wait; he summoned the attendant. 

"I took half-an-hour to learn this mantra; you must be mad to ask for one year"- the king yelled and continued: "Not only have I memorized it, but also got a priest to confirm that my delivery is fine. All it took was an hour. One may ask for 2 days or 3 days to learn this- but 1 year; you should be mad or you take me to be a bloody fool" 

The attendant could clearly see that the king was angry; he said- "my lord, if only you give me ten minutes and forgive my actions, I may explain" 

The king agreed. 

The attendant asked two servants of the court to bring a rope; when it was brought, he asked them to tie the king to the pillar with the rope. 

The servants did not move an inch but looked at the king and then looked around at others in the court. 

Everyone was watching with great fear, worried about the fate of the attendant. 

The attendant repeated his order to the servants in louder voice, again and again. 

Unable to take it anymore, the king shouted- "arrest this bloody chap" 

The whole court fell into silence and the attendant was arrested in a nano-second. 

The old minister then came forward and asked them to release the attendant. The servants looked at the king. The king nodded his head and they released the attendant. 

The old minister spoke ' "My lord, isn't the whole matter clear? We all asked the servants to do a thing. When the attendant asked them to tie you with a rope, they did not do it; but when you said the very same words, they instantly obeyed. 
When I asked them to release the attendant, they did not do; but only on your nod, they released him. 
Your words or nod have the power to call for obedience. It is not simply saying something- it is not even repetition of words that alone produces the effect- there should be, within those words, a power that gives the words the required strength. 
Mantra requires not only simple repetition; it requires other things to go with - such as oneness of mind, dedication, sincerity etc. That is why there is a belief that certain mantras should be learnt through a guru" 

The attendant got his leave.