Srila Bhaktisiddhanta Saraswati Thakura gave his disciples the sacred thread and Brahma Gayatri for both socioreligious and spiritual reasons. He incorporated this practice into his Gaudiya mission because hereditary Brahmanas were at that time still viewed as respectable representatives of the Hindu religion. In consideration of this socioreligious circumstance, Srila Bhaktisiddhanta had his initiated disciples wear the sacred thread regardless of whether or not they had been born in Brahmana families. This was his way of teaching that Vaishnavas, regardless of caste, were as respectable as Brahmanas, a point that many people did not understand.
As much as the sacred thread is still considered respectable is as much value as it has for preaching purposes. In the West the importance of wearing it for outreach purposes is negligible, but the sacred thread still seems to be an honored religious symbol in India. At this time the primary significance of wearing the sacred thread in Gaudiya Vaishnavism has to do with how followers of Srila Bhaktisiddhanta Saraswati Thakura Prabhupada identify it with the spirit of their missions. Considering the sacred thread an expression of discipleship and subordination to the acaryas gives spiritual meaning to wearing the sacred thread even if for preaching purposes its value might have diminished.
A devotee of Sri Caitanya Mahaprabhu can also consider wearing the sacred thread as part of their spiritual identity (svarupa) in Gaura-lila, as Gaudiya acaryas have determined that devotees of Sri Caitanyadeva are destined to serve as brahmana boys in that realm. If we think of the Brahma Gayatri in this light, we will be chanting it forever. In this way a socioreligious consideration can rise to a spiritual one. Whenever the socioreligious and the spiritual unite, that is a plus; whenever they part, we should follow the spiritual consideration with no loss.
One might also question the need for Brahma Gayatri when our principal mantras, Gopala Mantra and Kama Gayatri, are given at initiation (diksa), but one should not question the spirituality of Brahma Gayatri. Brahma Gayatri has a broader appeal than the Gopala Mantra and Kama Gayatri, but scripturally adept Gaudiya Vaishnavas know that Brahma Gayatri is much more than a mere sun mantra. Brahma Gayatri is only about the sun in as much as the sun is used as a conceptual symbol representing Brahman (God). The sun is equated with Brahman because everything in this world that we require for sustenance is dependent on the sun. Some Hindus certainly conceive of Brahma Gayatri as a sun mantra, but that is because they do not understand the full import of the mantra.
According to Sri Jiva Goswami, Brahma Gayatri petitions no one other than Bhagavan replete with his sakti. He is very clear on this in his Tattva-sandarbha. Scripture also acknowledges that Gayatri Mantra emanates from the flute of Sri Krishna, and the Garuda Purana clearly states that Srimad-Bhagavatam is a commentary on the Gayatri Mantra. As Srimad-Bhagavatam is a meditation on the supreme truth—satyam param dhimahi—so too is Gayatri. The Bhagavatam‘s opening statement indicates that the pastimes of Radha-Krishna (param) should be eternally (satyam) meditated upon (dhimahi).
All Gayatri mantras, including Kama Gayatri, come from the prototype of Brahma Gayatri, and it is said that Gayatri devi incarnated as Kama Gayatri in order to pursue gopi bhava. Kama Gayatri merely focuses more directly on the highest reach of Brahma Gayatri. Gopi bhava must be within Brahma Gayatri, as it is not possible for something to contain more than its source. Gayatri Mantra’s identification with Srimad-Bhagavatam and the transcendental sound emanating from the flute of Sri Krishna, as well as the fact that Kama Gayatri comes from Brahma Gayatri, should resolutely establish the spiritual nature of Brahma Gayatri.