A Kṛṣṇa conscious person has realized knowledge, by the grace of Kṛṣṇa, because he is satisfied with pure devotional service. By realized knowledge, one becomes perfect. By transcendental knowledge one can remain steady in his convictions, but by mere academic knowledge one can be easily deluded and confused by apparent contradictions. It is the realized soul who is actually self-controlled, because he is surrendered to Kṛṣṇa. He is transcendental because he has nothing to do with mundane scholarship. For him mundane scholarship and mental speculation, which may be as good as gold to others, are of no greater value than pebbles or stones.
(Bhagavad-gita--6:8---purport).

Only the self-controlled can gradually be attached to the Supreme Personality of Godhead. Self-controlled means not indulging in sense enjoyment more than is necessary. And those who are not self-controlled are given over to sense enjoyment. Dry philosophical speculation is a subtle sense enjoyment of the mind. Sense enjoyment leads one to the path of darkness. Those who are self-controlled can make progress on the path of liberation from the conditional life of material existence. The Vedas, therefore, enjoin that one should not go on the path of darkness but should make a progressive march towards the path of light or liberation.
(Srimad-Bhagavatam--1:18:22---purport).

A pure devotee of the Lord automatically develops all godly qualities, and some of the prominent features of those qualities are as follows: he is kind, peaceful, truthful, equable, faultless, magnanimous, mild, clean, nonpossessive, a well-wisher to all, satisfied, surrendered to Kṛṣṇa, without hankering, simple, fixed, self-controlled, a balanced eater, sane, mannerly, prideless, grave, sympathetic, friendly, poetic, expert and silent.
(Srimad-Bhagavatam--2:3:13---purport).