Which purana is known as the book of messenger-god and includes duties of people ofvarious varnas & ashrams and the importance of fasting

The Purana known as the "book of messenger-god" that includes the duties of people of various varnas (social classes) and ashrams (stages of life), as well as the importance of fasting, is the Bhagavata Purana.

The Bhagavata Purana is one of the eighteen Mahāpurāṇas and is primarily focused on the life and teachings of Lord Krishna. It elaborates on the principles of dharma, detailing the ethical responsibilities of individuals based on their varna and ashrama. Additionally, it emphasizes the significance of fasting and devotion, particularly in the context of achieving spiritual goals.

This text plays a crucial role in Hindu philosophy and presents a systematic approach to living a righteous life aligned with spiritual teachings.