What is the ultimate benefit of Kumbha Mela festival?

Kṛṣṇa will conquer the whole heart

“Hear about Krishna from someone who has real love and affection for Krishna, substantially, and when that enters your heart the flag of Krishna conception will be planted in that soil and ultimately spread its influence and claim the heart in the ultimate victory.”

Spiritual strength

Spiritual life is the ultimate battle. It's not for weak-minded, impendent people. This is the ultimate noble fight, noble struggle. So, brave act to admit once, to candidly admit, doinya atma-nivedanam, that not only I can't help others, I cannot help myself. That's not a sign of weakness, it takes courage to make that statement.