In Jain cosmology, time is cyclic and is divided into large time spans called kalpas. Each kalpa is split into two halves: utsarpini (ascending) and avasarpini (descending). In every half-cycle there are 24 Tirthankaras (ford-makers) who appear in succession to teach the dharma, establish the Jain sangha, and guide beings toward liberation. This fixed count of 24 is a traditional rule in Jain scriptures.

Key points:

• A kalpa contains both halves; in each half, 24 Tirthankaras arise.
• We are currently in a descending half-cycle (avasarpini); Mahavira is regarded as the 24th Tirthankar of this half-cycle.
• The 24 Tirthankaras are recognized across major Jain traditions (Digambara and Śvetāmbara), though their lists sometimes differ in minor details or naming conventions.

In short: 24 is a standard, canonical number in Jain cosmology for each half-cycle of time, rather than a number chosen for a particular reason beyond tradition.