Who is Vastu Purush & Why do we worship him ?

There is a story in Matasya Purana . Long  ago Lord Shiva fought against the demon named ANDHAKASUR and killed him. While fighting with demon, Shiva was very much tired and began to sweat profusely. A man was born of the drops of Shiva's sweat. He looked very cruel. He was very hungry. So he began to make penance to appease Lord Shiva and get a boon from him. Shiva was pleased with his penance and appeared before him.The devotee prayed to Shiva,"Oh Lord! Please permit me to eat away all the three worlds." Shiva said," Let it be so." The devotee's joy knew no bounds. He got possession on all the three worlds and first he was ready to eat the terrestrial world (Bhooloka). Then the celestial (Devatas), Brahma, Shiva and the demons (Rakshasas) also were terrified and caught hold of the devotee encircling him.

Forty-five celestial beings, out of whom 32 from without and 13 from within caught hold of the devotee. The Thirty-two celestial beings are-

(1) ISH (2) PAROJAYA (3) JAYANT (4) INDRA (5) SURYA (6) SADYA (7) BARISHAM (8) AKASH (9) AGNI (10) PUSHNA (11) VITATHA (12) YAMA (13) KRITANTA (14) GANDHARVA (15) BRINGAVAJA (16) MRIGA (17) PITARA (18) DAREPALE (19) SUGRIVA (20) PUSHPADANTA (21) VARUNA (22) DAITYA (23) SESHA (24) YAKSHMA (25) ROGA (26) NAGA (27) MUKHYA (28) BHALLATA (29) SOMA (30) SARPA (31) ADITI and DITI.

All these 32 celestial beings are out of the limits of the devotee whereas the following 13 Beings are within his limits:-

(1) BRAHMA (2) RUDRA (3) INDRAJAYA (4) APAVATSA (5) MARICHI (6) SAVITRI (7) VIVASWAN (8) VISHNU (9) MITRA (10) SAVITA (11) PRITHVIDHARA (12) RUDRA and (13) APA.

These celestial Beings laid force on the different limbs of the devotee and sat on them as shown below:

ISH (AGNI) – head; APA – face; PRITHWI DHARA & ARYAM – Chest; AVANTSA – heart; DITI & INDRA – Shoulders; SURYA & SOMA – Hands; RUDRA & RAJAYAKSHMA – left arm; SAVITRA & SAVITA – right arm; VIVASWAN & MITRA – Stomach; PUSHA & ARYAMA – Wrist; ASUR & SESHA – left side; VITATHA & GRAHAKSHAT – right side; YAMA & VARUNA – Thighs; GANDHARVA & PURAMADAN – on the knees; SUGRIV & BHRISH – shanks; DWARIKA & MRIGA – ankles; JAYA & SHAKRA – on the hairs grown on the feet; BRAHMA – on the heart.

 Vaastu Purusha, being arrested like this, said to the Gods, "Oh, Celestial Beings! You have all caught holdof me and tied me on all the sides. How long shall I be like this, in this position hanging my head down like a prisoner? What shall I eat? Listening to those words, Lord Brahma  said,Today is Bhadrapada Shukla Triteya Saturday and 'Visakha Star'; So you lie down here on the ground changing your position once in three months, i.e. from 'Bhadraspada' to 'kartik' you lie down putting your head in the eastern direction and your feet towards the west. During the months of "Margashira", 'Pusham' and 'Magha', you lie down towards the south looking towards the west and put your feet towards the north during the months of 'Phalgun', 'Chaitra' and 'Vaisakh' put your head towards the west and feet towards the east., looking towards the north; in the months of 'Jyestha', 'Ashadha' and 'Sravana', put your head towards the east. North and the feet towards the south & look towards the east. Whatever side you may turn, you will have to lie down on the left side only. You will be known as 'VASTU PURUSHA'.
And all mankind will worship you as a God of Vastu and the people will donate you some food.

In such Vastu, you will be responsible for the well being, happiness and prosperity of your worshipers.