In Hindu culture Ganapati is worshiped first before starting any Puja or major works. Lord Ganpati is indicated by His elephant head, enormous belly, His mount and a little mouse. Ganpati is god of wisdom and knowledge. He is the Vighnaharta (one of the Ashtavinayaka) or the god who removes all obstacle.
According to Ganpati Upanishad, Lord Ganesha is endless and He seemed even before the procedure of creation and consciousness. This is one of the important reasons why Ganapati is worshiped first in Hindu culture before starting any Puja.
The Mythological theory
According to dharmik shashtra’s popularly known as hindu mythological, Goddess Parvati ordered Ganesha to guard the gate and stop anyone who attempts to enter. Lord Shiva got there and attempted to enter the room and Lord Ganpati who was guarding the gate stopped lord shiva. But, the little Ganapati did not permit the entry. Hence, Lord Shiva beheaded his little boy out of anger.
Goddess Parvati came out as Ganesha began screaming because of pain and saw his boy’s depressing plight. Goddess Parvati got angry and menaced to damage the world if his boy’s head is not restored again. Seeing the wrath of the Goddess Parvati, Lord Shiva changed the head of ganpati with elephant and Lord Ganesha’s life restored.
Shiva realized the Ganesha’s situation and Parvati’s disappointment. Hence, he bestowed Lord Ganapati that no puja might be finished earlier than Lord Ganpati is worshipped. He also blessed with the enormous divine power to Lord Ganesha.
Another mythological theory
Once Kartikeya the elder brother of Lord Ganesha declared that he’s the wise God amongst all the Gods. But, Lord Shiva recommended to each the brothers to encircle the universe.
The one will be declared the winner who encircled the universe first. Lord Kartikeya commenced encircling the universe with the aid of taking his peacock. While Lord Ganesha commence encircling Lord Shiva and Goddess Parvati considering the parents as his universe.
By seeing Lord Ganesha’s intelligence Lord Shiva declared him as the winner. Due to the fact then Lord Ganesha is being worshipped first.