Radhanath Swami: Lord Krishna explains in the Bhagavad Gita that without controlling the mind and the senses there is no question of real yoga or real spiritual practice. To do anything good in life or to succeed, discipline is required. To be a good musician, you have to discipline yourself and practice for so many hours everyday for so many years. To be a good student you have to discipline yourself to study the books, to go to the classes, etc. To be a good athlete you have to discipline yourself to train your body. Similarly, in business there must be certain amount of discipline, in politics there must be a certain amount of discipline.
But the highest gain, the highest ideal that a human being can strive for is self-realization, spiritual enlightenment that culminates in prem bhakti, love of God. And obviously, even for that there must be discipline. Vaidhi bhakti means we discipline ourselves. We accept what is favorable for spiritual advancement and we reject what is unfavorable. The mind wants to speak all nonsense things, we discipline it by speaking useful things; the mind wants the body to engage in immoral activities, we discipline it by saying no and engaging it in proper activities; the mind wants to oversleep, we discipline it to not waste time. Krishna explains in Gita that those on the path of yoga neither sleep too much nor sleep too little; they neither eat too much nor do they eat too little. We should regulate ourselves in such a way that we can actually make progress. So yes, discipline is very important.
Discipline is not a painful dry thing if we are doing it with the proper idea. We should be dynamic, we should be energetic, and we should be enthusiastic for the right things. Srila Prabhupada, our guru, would say that Krishna consciousness is a positive alternative to give up the lower things. We accept higher principles and keep our mind focused on that. It’s the road to eternal happiness.