Why is it mandatory to worship Lord Ganesh during initiation of any other worship in Hinduism?

In Hinduism, there are five prime god called as panch dev (Five god). The name of those five gods are Lord Vishnu, Lord Shiva, Lord Ganesh, Lord Surya (Sun) and the godess Durga. Among these five gods, Lord Ganesh have their own significance. Lord Ganesh is considered as first worship able before the worship of any other God or Godess. Hence Lord Ganesh is called as "Pratham Pujan". Meaning of Ganesh name is chief of the group or leader of the group. If we try to understand that the mind (Mann) controls the body.  Body is the group and mind is the leader of whole body. Hence it can be said that the Lord Ganesh is the god of mind or mental powers.
       In ashtang yog (eight part yog), yogi concentrate on different spiritual wheels, which are present in human body to increase the power and to achieve spiritual upliftment. There are seven spiritual wheels in human body. Those are Mool dhara chahta, Swadhisthan chakra, Manipur chakra , Anahad chakra , Vishudh chakra , Aagya chakra. Among these chakra, Aagya chakra is most significant chakra because it controls other chakra. As I said that Lord Ganesh is the god of mental power. Hence, for concentration and feeling during Pooja, Lord Ganesh is worshipped first. In any Pooja, without concentration and feeling, it is considered that there is no advantages or achievement by performing any worship.
           Ashtang yogis practice to concentrate on third eye (Aagya chakra). It is nothing but a kind of worship to Lord Ganesh. Lord Shiva and even Goddess Parvati having third eye means they have Lord Ganesh as their son. According to puranas, Lord Ganesh have not born as per Brahma created nature or sexually. Lord Ganesh has been born through psychic energy of Godess Parvati. Lord Shiva alway practices shambhavi mudra mean practicing concentration on third eye. Hence Lord Shiva has complete control over the third eye and called as Shambhoo.

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