Name of god is a support for Devotee to do sumiran,  dhyan, kirtan  and go beyond to the parabrahma/prabhu ..at that level their chosen god is prabhu , the nirgun nirakar, without nama rupa . these vanish

Krishna,  rama or any ista devatha has certain qualities described by the names .. and devotee when takes a name , that quality blossoms in the personality of devotee …..thus devotee invites god/ god’s qualities into himself and he becomes that god, and ultimately his own inner self is experienced as paramatma

For some their guru is parabrahma …it all depends on intensity of sadhana , and the level of purity gained in the body mind nervous system