Step 1: Understanding the Concept:
The question asks about the core philosophical or religious concept behind the design of Persian gardens.
Step 2: Detailed Explanation:
The design of Persian gardens is deeply symbolic and is intended to represent paradise or Heaven on Earth. The traditional 'Charbagh' style, divided into four quadrants by water channels, symbolizes the four rivers of Paradise mentioned in the Quran. Water, shade, and lush greenery in an otherwise arid landscape represent the abundance and serenity of Heaven. This concept was inherited and adapted by the Mughals for their gardens in India. The design is a physical manifestation of a spiritual ideal.
Step 3: Final Answer:
Persian gardens are based on the idea of Heaven (Paradise).