SB 3.25.19

na yujyamānayā bhaktyā
 bhagavaty akhilātmani
sadṛśo ’sti śivaḥ panthā
 yogināṁ brahma-siddhaye
Word for word: 
na — not; yujyamānayā — being performed; bhaktyā — devotional service; bhagavati — towards the Supreme Personality of Godhead; akhila-ātmani — the Supersoul; sadṛśaḥ — like; asti — there is; śivaḥ — auspicious; panthāḥ — path; yoginām — of the yogīs; brahma-siddhaye — for perfection in self-realization.
Translation: 
Perfection in self-realization cannot be attained by any kind of yogī unless he engages in devotional service to the Supreme Personality of Godhead, for that is the only auspicious path.
Purport: 

That knowledge and renunciation are never perfect unless joined by devotional service is explicitly explained here. Na yujyamānayā means “without being dovetailed.” When there is devotional service, then the question is where to offer that service. Devotional service is to be offered to the Supreme Personality of Godhead, who is the Supersoul of everything, for that is the only reliable path of self-realization, or Brahman realization. The word brahma-siddhaye means to understand oneself to be different from matter, to understand oneself to be Brahman. The Vedic words are ahaṁ brahmāsmi. Brahma-siddhi means that one should know that he is not matter; he is pure soul. There are different kinds of yogīs, but every yogī is supposed to engage in self-realization, or Brahman realization. It is clearly stated here that unless one is fully engaged in the devotional service of the Supreme Personality of Godhead one cannot have easy approach to the path of brahma-siddhi.

In the beginning of the Second Chapter of Śrīmad-Bhāgavatam it is stated that when one engages himself in the devotional service of Vāsudeva, spiritual knowledge and renunciation of the material world automatically become manifest. Thus a devotee does not have to try separately for renunciation or knowledge. Devotional service itself is so powerful that by one’s service attitude, everything is revealed. It is stated here, śivaḥ panthāḥ: this is the only auspicious path for self-realization. The path of devotional service is the most confidential means for attaining Brahman realization. That perfection in Brahman realization is attained through the auspicious path of devotional service indicates that the so-called Brahman realization, or realization of the brahmajyoti effulgence, is not brahma-siddhi. Beyond that brahmajyoti there is the Supreme Personality of Godhead. In the Upaniṣads a devotee prays to the Lord to kindly put aside the effulgence, brahmajyoti, so that the devotee may see within the brahmajyoti the actual, eternal form of the Lord. Unless one attains realization of the transcendental form of the Lord, there is no question of bhakti. Bhakti necessitates the existence of the recipient of devotional service and the devotee who renders devotional service. Brahma-siddhi through devotional service is realization of the Supreme Personality of Godhead. The understanding of the effulgent rays of the body of the Supreme Godhead is not the perfect stage of brahma-siddhi, or Brahman realization. Nor is the realization of the Paramātmā feature of the Supreme Person perfect, for Bhagavān, the Supreme Personality of Godhead, is akhilātmā — He is the Supersoul. One who realizes the Supreme Personality realizes the other features, namely the Paramātmā feature and the Brahman feature, and that total realization is brahma-siddhi.