When a touchstone touches iron, it turns the iron to gold. Parvata Muni called Nārada Muni a touchstone because by his touch the hunter, who was lowest among men, became an elevated and perfect Vaiṣṇava. Śrīla Bhaktivinoda Ṭhākura said that the position of a Vaiṣṇava can be tested by seeing how good a touchstone he is-that is, by seeing how many Vaiṣṇavas he has made during his life. A Vaiṣṇava should be a touchstone so that he can convert others to Vaiṣṇavism by his preaching, even though people may be fallen like the hunter. There are many so-called advanced devotees who sit in a secluded place for their personal benefit. They do not go out to preach and convert others into Vaiṣṇavas, and therefore they certainly cannot be called sparśa-maṇi, advanced devotees. Kaniṣṭha-adhikārī devotees cannot turn others into Vaiṣṇavas, but a madhyama-adhikārī Vaiṣṇava can do so by preaching. Śrī Caitanya Mahāprabhu advised His followers to increase the numbers of Vaiṣṇavas.

(Cc. Madhya 7.128)

It is Śrī Caitanya Mahāprabhu's wish that everyone should become a Vaiṣṇava and guru. Following the instructions of Śrī Caitanya Mahāprabhu and His disciplic succession, one can become a spiritual master, for the process is very easy. One can go everywhere and anywhere to preach the instructions of Kṛṣṇa. Bhagavad-gītā is Kṛṣṇa's instructions; therefore the duty of every Vaiṣṇava is to travel and preach Bhagavad-gītā, either in his country or a foreign country. This is the test of sparśa-maṇi, following in the footsteps of Nārada Muni.