Prabhupada Letters :: 1968.

"Simply by understanding Krishna, one understands everything. Therefore, Krishna being the Supreme Spirit, one who tries to understand Krishna, he can understand everything else."

Prabhupada Letters :: 1969.

"Even Lord Krishna, Lord Caitanya, and what to speak of other acaryas, all of them accepted a bona fide Spiritual Master. Aroha means to try to understand God by one's own effort, and avaroha means to understand God by disciplic succession."