Explanation:

- Festivals often bring people together from different backgrounds, celebrating unity amid their varied experiences and traditions.

- Option 1: Richness - While festivals are often rich in color and tradition, "unity in richness" does not capture the essence of varied backgrounds coming together.

- Option 2: Belongingness - This implies feeling accepted and part of something, but it doesn't specifically address varying backgrounds.

- Option 3: Diversity - This is about differences living harmoniously, which perfectly complements "unity."

- Option 4: Inclusion - Implies involvement and acceptance, but isn't as focused on variances as "diversity."