Question: Is it permissible to chant other Mantras or worship other deities along with Gayatri ?
Central theme of any form of worship is meditation. The exclusive objective of Jap and meditation in Upasana is to establish an intimate emotional bond between the devotee and God .Spirituality in India permits a free choice amongst a multitude of symbols (as deities) for meditating on attributes of the Creator. Once a particular deity is chosen as one’s Ishtadeo (Exclusive representative deity for worship), it is considered mandatory to follow the rituals and Mantras of Upasana pertaining to the Ishtadeo only and pursue Upasana - Sadhana - Aradhna strictly according to the procedure laid down by the Guru . During Sadhana , the Ishtadeo is treated like a living person, as one’s most intimate relative, as father - mother - brother - helper - master - friend, all rolled into one (Twameva Mata-cha, Pita Twameva....). Only after cultivating such an intimate relationship with God , can one expect His / Her grace.
Because of ignorance, many devotees decorate their place of worship with assorted forms, (photographs etc.) of deities, chant many Mantras and say prayers to please them. Disregarding the Oneness of God (Brahma), they try to establish some relationship with many deities in expectation of multifarious benefits from each of them. In the field of spirituality such a practice becomes counterproductive. The deities represent streams of that ‘One fountainhead’ of God . Interaction with some particular attributes of God (deity) may be necessary for a particular purpose, but for an all-round spiritual progress one should choose Gayatri as Ishtadeo. (Ref. Upasana Ke Do Charan Jap or Dhyan).