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Rāja-vidyā: The King of Knowledge
Kṛṣṇa consciousness can be attained in one second, or it cannot be had even after a thousand births and deaths. If we choose, we can immediately become great souls by surrendering to Kṛṣṇa, but because we have doubts whether or not Kṛṣṇa is actually the Supreme we have to take time to dissipate these doubts through study of the scriptures. By studying  Bhagavad-gītā  under the guidance of a bona fide spiritual master, we can remove these doubts and make definite progress.
It is the fire of knowledge that burns all doubts and fruitive activities to ashes. Śrī Kṛṣṇa gives the following information of the results of inquiring of the truth from one who has actually seen the truth.
yaj jñātvā na punar moham 
    evam yāsyasi pāṇḍāva 
    yena bhūtany aśeṣāṇi 
    drakṣyasy ātmany atho mayi 
    api ced asi pāpebhyaḥ 
    sarvebhyaḥ pāpa-kṛttamaḥ 
    sarvam jñāna-plavenaiva 
    vṛjinam santariṣyasi 
    yathaidhāmsi samiddho 'gnir 
    bhasmasāt kurute 'rjuna 
    jñānāgniḥ sarva-karmāṇi 
    bhasmasāt kurute tathā
“And when you have thus learned the truth, you will know that all living beings are but parts of Me—and that they are in Me, and are Mine. Even if you are considered to be the most sinful of all sinners, when you are situated in the boat of transcendental knowledge, you will be able to cross over the ocean”