Agni is both the sacred fire as well as deity of that hearth who transmits oblations to another deities. Hence, this mantra is recited even though invoking the deity Agni in the form of hearth as witness towards the vow. Agne vratapate vrataṃ cariṣyāmi (Vājasaneyī-Saṃstrikeā of the Śukla [White] Yajurveda https://freedirectory4u.com/listings13291527/the-basic-principles-of-baglamukhi