When we speak of transcendental knowledge, we do so in terms of spiritual understanding. As such, there is nothing so sublime and pure as transcendental knowledge. Ignorance is the cause of our bondage, and knowledge is the cause of our liberation. This knowledge is the mature fruit of devotional service, and when one is situated in transcendental knowledge, he need not search for peace elsewhere, for he enjoys peace within himself. In other words, this knowledge and peace culminate in Kṛṣṇa consciousness. That is the last word in the Bhagavad-gītā.
(Bhagavad-Gita-4:38-purport).

There are many devotees who assume themselves to be in Kṛṣṇa consciousness and devotional service but at heart do not accept the Supreme Personality of Godhead, Kṛṣṇa, as the Absolute Truth. For them, the fruit of devotional service—going back to Godhead—will never be tasted. Similarly, those who are engaged in fruitive pious activities and who are ultimately hoping to be liberated from this material entanglement will never be successful either, because they deride the Supreme Personality of Godhead, Kṛṣṇa. In other words, persons who mock Kṛṣṇa are to be understood to be demonic or atheistic. As described in the Seventh Chapter of Bhagavad-gītā, such demonic miscreants never surrender to Kṛṣṇa. Therefore their mental speculations to arrive at the Absolute Truth bring them to the false conclusion that the ordinary living entity and Kṛṣṇa are one and the same. With such a false conviction, they think that the body of any human being is now simply covered by material nature and that as soon as one is liberated from this material body there is no difference between God and himself. This attempt to become one with Kṛṣṇa will be baffled because of delusion. Such atheistic and demoniac cultivation of spiritual knowledge is always futile. That is the indication of this verse. For such persons, cultivation of the knowledge in the Vedic literature, like the Vedānta-sūtra and the Upaniṣads. is always baffled.
(Bhagavad-Gita-9:12-purport).

To taste the fruit of devotional service in Goloka Vṛndāvana is the highest perfection of life, and in the presence of such perfection, the four material perfections—religion, economic development, sense gratification and liberation—are very insignificant achievements.
(Sri Caitanya Caritamrta-2:19:164-translation).

In many places devotional service has been compared to a creeper. One has to sow the seed of the devotional creeper, bhakti-latā, within his heart. As he regularly hears and chants, the seed will fructify and gradually grow into a mature plant and then produce the fruit of devotional service, namely love of Godhead, which the gardener (mālā-kāra) can then enjoy without impediments.
(Sri Caitanya Caritamrta-1:9:9-purport).