One requires spiritual strength in order to understand Krishna and to enter the spiritual world. Prabhupada says that we are not talking about physical strength. Spiritual strength is the strength to overcome the influence of the modes of material nature, to cross the ocean of material existence, and to become qualified to enter into that supreme abode which is unmanifest and infallible.
Transcription of a Lecture Given on Balarama Purnima, August 26, 2018, in Almaty, Kazakhstan