This is the correct way of understanding Bhagavad-gītā, and this is called śraddhā. It is not that one accepts a portion of Bhagavad-gītā according to his own whimsical interpretations and then rejects another portion. This is not śraddhā. Śraddhā means accepting the instructions of Bhagavad-gītā in their totality, especially the last instruction: sarva-dharmān parityajya mām ekaṁ śaraṇaṁ vraja. "Abandon all varieties of religion and just surrender unto Me." (BG 18.66) When one becomes completely faithful in regard to this instruction, one's strong faith becomes the basis for advancing in spiritual life.
When one fully engages in chanting the Hare Kṛṣṇa mahā-mantra, he gradually realizes his own spiritual identity. Unless one faithfully chants the Hare Kṛṣṇa mantra, Kṛṣṇa does not reveal Himself: sevonmukhe hi jihvādau svayam eva sphuraty adaḥ. (Bhakti-rasāmṛta-sindhu 1.2.234) We cannot realize the Supreme Personality of Godhead by any artificial means. We must engage faithfully in the service of the Lord. Such service begins with the tongue (sevonmukhe hi jihvādau), which means that we should always chant the holy names of the Lord and accept kṛṣṇa-prasāda. We should not chant or accept anything else. When this process is faithfully followed, the Supreme Lord reveals Himself to the devotee.
When a person realizes himself to be an eternal servitor of Kṛṣṇa, he loses interest in everything but Kṛṣṇa's service. Always thinking of Kṛṣṇa, devising means by which to spread the holy name of Kṛṣṇa, he understands that his only business is in spreading the Kṛṣṇa consciousness movement all over the world. Such a person is to be recognized as an uttama-adhikārī, and his association should be immediately accepted according to the six processes (dadāti pratigṛhṇāti, etc.). Indeed, the advanced uttama-adhikārī Vaiṣṇava devotee should be accepted as a spiritual master. Everything one possesses should be offered to him, for it is enjoined that one should deliver whatever he has to the spiritual master. The brahmacārī in particular is supposed to beg alms from others and offer them to the spiritual master. However, one should not imitate the behavior of an advanced devotee or mahā-bhāgavata without being self-realized, for by such imitation one will eventually become degraded.
In this verse Śrīla Rūpa Gosvāmī advises the devotee to be intelligent enough to distinguish between the kaniṣṭha-adhikārī, madhyama-adhikārī and uttama-adhikārī. The devotee should also know his own position and should not try to imitate a devotee situated on a higher platform. Śrīla Bhaktivinoda Ṭhākura has given some practical hints to the effect that an uttama-adhikārī Vaiṣṇava can be recognized by his ability to convert many fallen souls to Vaiṣṇavism. One should not become a spiritual master unless he has attained the platform of uttama-adhikārī. A neophyte Vaiṣṇava or a Vaiṣṇava situated on the intermediate platform can also accept disciples, but such disciples must be on the same platform, and it should be understood that they cannot advance very well toward the ultimate goal of life under his insufficient guidance. Therefore a disciple should be careful to accept an uttama-adhikārī as a spiritual master.