Then why is it that Yavana Vaisnavas is not permitted to worship and serve the Deities in the Vaisnava temples? Moreover, what about the brahmanas?.
It is an offense to refer to a Vaisnava as a Yavana, simply because he has taken birth in such a family. All Vaisnavas have the right to serve Krishna. If a grhastha Vaisnava serves the Deity in a way that breaks the rules of varnasrama, it is considered to be a fault from the worldly point of view.
Nirapeksa Vaisnavas (a renounced Vaisnava who is indifferent to all social restrictions is known as nirapeksa; without any needs or requirements), are not required to worship the Deity, because that would hinder their quality of being free from all external requirements and dependencies (nirapeksata). They remain engaged in serving Sri Radha-Vallabha through service carried out by the internally-conceived spiritual form,manasi-seva (.to serve God seva, using for that the power of mind, manasi).
Moreover, what about the brahmanas?.
There are two types of brahmanas: brahmanas by nature (svabhava-siddha) and brahmanas by birth alone (jatisiddha).
Those who are brahmanas by nature should be respected by adherents of all philosophical systems because they are practically Vaisnavas.
Those who are only brahmanas by birth are given conventional respect by everyone, and this is also approved by the Vaisnavas.
The conclusion of the scripture on this topic is expressed in Srimad-Bhagavatam (7.9.10):
“A bhakta who is born in a family of dog-eaters, but who has dedicated his mind, words, activities, and wealth at the lotus feet of Krishna, is superior to a brahmana who has all twelve brahminical qualities, but who is averse to the lotus feet of Bhagavan, whose navel is shaped like a lotus. Such a bhakta can purify himself and his whole family, whereas the brahmana who is puffed-up with false prestige cannot even purify himself. That is my opinion.”