Answer in Details
Several reasons explain why Lord Shiva is addressed as Mahadev:
1. Supreme Power: Shiva is considered the Adi Yogi, the original yogi, and the source of all energies. He is beyond birth and death, and his power encompasses the entire cosmos.
2. Master of All Gods: Scriptures like the Shiva Purana and various Upanishads describe Shiva as the lord whom even other gods such as Vishnu and Brahma worship.
3. Embodiment of Compassion: Despite his immense power, Shiva is known for his compassion and grace. He grants boons to his devotees easily and is known as Ashutosh (one who is easily pleased).
4. Symbol of Renunciation and Balance: Shiva represents the perfect balance between asceticism and worldly life, destruction and creation, meditation and action.
5. Destroyer of Evil: As Mahadev, Lord Shiva destroys ignorance, ego, and evil, helping beings attain liberation (moksha).
In summary, Lord Shiva is called Mahadev because he is worshipped as the highest and most powerful deity, the God of all gods, embodying both the destructive and regenerative aspects of the divine.