Answer
Ultimately, lasting transformation comes when perception changes, because then behavior changes naturally and permanently.
If your perception remains the same but you forcibly restrain your behavior, that is still helpful, but it is only a temporary solution. For example, you know that certain activities are against devotional service because your spiritual master has instructed you not to engage in illicit sex, intoxication, and other sinful activities. Initially, you may not fully understand or realize why these instructions are given.
Even without complete realization, you follow them out of faith. By chanting the holy name, you receive the strength to practice self-restraint. In the beginning, your practice is sustained by faith rather than mature realization.
For example, in brahmacharya, you may not yet fully understand how material desires are manifestations of maya. Nevertheless, you follow the rules because they have been given by the spiritual master. As you continue chanting Hare Krishna, true spiritual understanding awakens.
Once genuine realization develops, you naturally lose attraction to those activities. At that stage, self-restraint is no longer necessary because there is no opposing force pulling you toward them.
A pure devotee does not constantly struggle with self-control. Everything is naturally seen in relation to Krishna and how it can be used in His service. When perception becomes completely purified, behavior naturally follows.
