Final answer:
Religion is a complex and varied subject that is difficult to define due to its diverse manifestations across cultures and its individual and social aspects.
Step-by-step explanation:
Religion is a complex and varied subject that can be challenging to define. It encompasses a wide range of beliefs, practices, and social structures across different cultures. The individual nature of religious experiences and the embeddedness of religion in social structures make it difficult to study as a single phenomenon. Additionally, religion cannot be approached solely from a scientific point of view and is not a subject for scientists.