aja Vidya Guhya Yoga:Bhagavad Gita Chapter 9 [Confidential Knowledge of the Ultimate Truth]
Krishna Said > Shaloka: 3
English
Those who are not faithful on the path of devotional service cannot attain Me, O conqueror of foes, but return to birth and death in this material world.
Purport
The faithless cannot accomplish this process of devotional service; that is the purport of this verse. Faith is created by association with devotees. Unfortunate people, even after hearing all the evidence of Vedic literature from great personalities, still have no faith in God. They are hesitant and cannot stay fixed in the devotional service of the Lord. Thus faith is a most important factor for progress in Krishna consciousness. In the Caitanya-caritamrta it is said that one should have complete conviction that simply by serving the Supreme Lord Sri Krishna he can achieve all perfection. That is called real faith. In the Srimad-Bhagavatam (3.4.12) it is stated that by giving water to the root of a tree, its branches, twigs and leaves become satisfied, and by supplying food to the stomach all the senses of the body become satisfied, and, similarly, by engaging in the transcendental service of the Supreme Lord, all the demigods and all the living entities automatically become satisfied.
After reading Bhagavad-gita one should promptly come to the conclusion of Bhagavad-gita: one should give up all other engagements and adopt the service of the Supreme Lord, Krishna, the Personality of Godhead. If one is convinced of this philosophy of life, that is faith. Now the development of that faith is the process of Krishna consciousness.