SB 3.27.22

jñānena dṛṣṭa-tattvena
 vairāgyeṇa balīyasā
tapo-yuktena yogena
 tīvreṇātma-samādhinā
Synonyms: 
jñānena — in knowledge; dṛṣṭa-tattvena — with vision of the Absolute Truth; vairāgyeṇa — with renunciation; balīyasā — very strong; tapaḥ-yuktena — by engagement in austerity; yogena — by mystic yoga; tīvreṇa — firmly fixed; ātma-samādhinā — by self-absorption.
Translation: 
This devotional service has to be performed strongly in perfect knowledge and with transcendental vision. One must be strongly renounced and must engage in austerity and perform mystic yoga in order to be firmly fixed in self-absorption.
Purport: 

Devotional service in Kṛṣṇa consciousness cannot be performed blindly due to material emotion or mental concoction. It is specifically mentioned here that one has to perform devotional service in full knowledge by visualizing the Absolute Truth. We can understand about the Absolute Truth by evolving transcendental knowledge, and the result of such transcendental knowledge will be manifested by renunciation. That renunciation is not temporary or artificial, but is very strong. It is said that development of Kṛṣṇa consciousness is exhibited by proportionate material detachment, or vairāgya. If one does not separate himself from material enjoyment, it is to be understood that he is not advancing in Kṛṣṇa consciousness. Renunciation in Kṛṣṇa consciousness is so strong that it cannot be deviated by any attractive illusion. One has to perform devotional service in full tapasya, austerity. One should fast on the two Ekādaśī days, which fall on the eleventh day of the waxing and waning moon, and on the birthdays of Lord Kṛṣṇa, Lord Rāma and Caitanya Mahāprabhu. There are many such fasting days. Yogena means “by controlling the senses and mind.” Yoga indriya-saṁyamaḥ. Yogena implies that one is seriously absorbed in the self and is able, by development of knowledge, to understand his constitutional position in relationship with the Superself. In this way one becomes fixed in devotional service, and his faith cannot be shaken by any material allurement.