In Jainism, fasting (upavasa) is a powerful form of tapas—self-discipline aimed at purifying the mind, speech, and body and reducing the inflow of karmas. The essence of longer fasting is to intensify renunciation and inner restraint so that one’s attachment to bodily comforts loosens and one can see reality more clearly.

Key points about the essence of longer fasting:

• Purification of karma: Prolonged fasting reduces activities that bind karmas and helps burn off subtle impurities accumulated through thoughts, words, and actions.
• Cultivation of restraint: It strengthens control over desires, senses, and ego, promoting humility, patience, and equanimity.
• Clarity of mind: With fewer external stimuli and cravings, one can cultivate greater concentration, discernment, and compassion.
• Right intention (bhav) and sincerity: The spiritual fruit of a long fast depends on pure intention, regular practices like reflection (pratikraman) and mindfulness (samayik), and non-violence in all forms.
• Health with prudence: Fasting should be undertaken with awareness of one’s health and strength, and it is common to adapt the practice to ensure it remains a safe, focused spiritual effort rather than self-harm.

Notes on practice:

• Longer fasts are treated as a serious vrata (discipline) and are normally guided by a respected Jain teacher or community elder.
• They are often paired with reflective practices (samayik), confession (pratikraman), and acts of compassion (dana) to deepen the spiritual effect.
• There are variations in how Digambar and Shwetambar traditions describe and practice prolonged fasts, but the core aim—reducing karmic bondage and advancing spiritual progress—remains the same.

If you’d like, tell me whether you want a brief or more detailed explanation, and I can provide a concise summary or a deeper, tradition-specific outline.