Nandi is not just Vehicle for Shiva, but Shiva's great devotee, Kailash’s gate keeper and His best friend :)
- Nandi was born to Sage Shilada, after doing rigorous penance for several years. When Nandi learns from his father, that he is short lived, he starts his tapasya for Shiva. Shiva, very happy with Nandi grants boon of him becoming His vehicle and grants him immortality. Nandi’s selfless devotion to Mahadev makes him the greatest devotee of God Shiva.
- When Devas and Asuras did Samudra Manthan, churning of the ocean for celestial nectar. Foremost, poison oozed out of the Ocean and Shiva drank the poison to save the Universe, and along with Shiva, Nandi too drank the poison but nothing happened to Nandi. Since Nandi surrendered to Shiva completely, he became an immortal.
- Shiva pleased with Nandi gave a boon that, whoever visits Shiva temple first have to pray to Nandi, please Him, and see Shivling through Nandi’s horns (the space between his two horns) and tell the purpose of their visit or wishes in Nandi’s ears, since it will for sure reach Shiva.
- According to few Puranas , Nandi has bull/Ox face and a Human body which symbolises that of Shiva(as Shankara and Pashupatinath). This means that Nandi can take the form of an Ox or any human form as per his wish. When Shiva wants to travel, then Nandi takes an Ox form and Shiva chose Ox as His mount since it is a hard working animal and is never lazy.
- The entire Universe resides in the Mahadev, and when Ravana lifted the Kailash mountain, Shiva just pressed His toe and Ravana’s hands get crushed under the mountain. So we can imagine the strength of the Mahadev. But Nandi can carry Shiva on him, as he has surrendered completely to Shiva, so because of Nandi's selfless devotion, he can carry the immense powerful Mahadev.
- Nandi is born only to do service to Shiva, so he doesn't want to miss even one second of seeing Shiva, so he always sits facing Shiva so that he doesn't miss even a blink of an eye moment of seeing, worshipping and doing service to his God Shiva.
Om Nandeeshwaraya Namaha
Om Swetha-vrishabha-vahanaya Namaha