Kubera was a simple man with a simple life who worshiped Lord Shiva for years. Years later, Shiva appeared to him and granted him all of the wealth in the world, the care taker of wealth. He was a man from modest means, so he was thrilled. All of the wealth in the world allowed him to fulfill every desire in life. However, he soon became mindless and greedy. He wanted to make more and more money and forgot he was just a caretaker and not the actual owner.
Shiva found out about Kubera’s misplaced greed and decided to teach him a lesson. He informed Kubera to host a feast and call on all the kings and Gods so they would get to know the importance of Kubera. Kubera hastily agreed. Shiva, unable to attend, sent his son Ganesha instead.
Lord Ganesha arrived with a furious appetite and ate all of the food Kubera prepared. This did not satisfy his appetite. With no food remaining, he started to feed on the palace Kubera lived in and then all of his accumulated wealth. Ganesha was still hungry after eating all of the wealth in the world, so he set his eyes on Kubera himself.
The story continues, but essentially from this event, Kubera realized how important it is to be humble in life. Not everyone has wealth and even those that do can lose it easily. Kubera became the symbol for one of the benefits of yantras: wealth. Anyone who worships him will always be prosperous. People now worship to the Kuber Yantra to attain wealth and prosperity and to regain lost wealth.