One who trains his subordinate or disciple to worship Vāsudeva is the truly bona fide spiritual master. The word jagad-gurum is very important in this regard. Kaśyapa Muni did not falsely declare himself to be jagad-guru, although he actually wasjagad-guru because he advocated the cause of Vāsudeva. Actually, Vāsudeva is jagad-guru, as clearly stated here (vāsudevaṁ jagad-gurum). One who teaches the instructions of Vāsudeva, Bhagavad-gītā, is as good as vāsudevaṁ jagad-gurum. But when one who does not teach this instruction—as it is—declares himself jagad-guru, he simply cheats the public. Kṛṣṇa is jagad-guru, and one who teaches the instruction of Kṛṣṇa as it is, on behalf of Kṛṣṇa, may be accepted as jagad-guru. One who manufactures his own theories cannot be accepted; he becomes jagad-guru falsely. (Srimad Bhagavatam---8:16:20---purport).

When one is completely fit to chant the holy name in this way, he is eligible to make disciples all over the world, and he actually becomes jagad-guru. Then the entire world, under his influence, begins to chant the holy names of the Hare Kṛṣṇa mahā-mantra. Thus all the disciples of such a spiritual master increase in attachment for Kṛṣṇa, and therefore he sometimes cries, sometimes laughs, sometimes dances and sometimes chants. (Sri Caitanya Caritamrta---1:7:83---purport).
A person who knows what is spiritual and what is material and who is firmly fixed in the spiritual position can be jagad-guru, the spiritual master of the entire world. One cannot become jagad-guru simply by advertising oneself as jagad-guru without knowing the essential principles for becoming jagad-guru. Even people who never see what ajagad-guru is and never talk with other people become puffed-up sannyāsīs and declare themselves jagad-gurus. Śrī Caitanya Mahāprabhu did not like this. Any person who knows the science of Kṛṣṇa and who is fully qualified in spiritual life can become jagad-guru. (Sri Caitanya Caritamrta--3:5:85---purport).

Śrīla Bhaktisiddhānta Sarasvatī Ṭhākura explains that unless one is directly empowered by the causeless mercy of Kṛṣṇa, one cannot become the spiritual master of the entire world (jagad-guru). One cannot become an ācārya simply by mental speculation. The true ācārya presents Kṛṣṇa to everyone by preaching the holy name of the Lord throughout the world.
(Sri Caitanya Caritamrta---3:7:12---purport).