Our vasanas decide the direction in which we will lead our life. If in one's past life one was addicted to alcohol, such vasana will not vanish on one's death. It will continue on his next birth also. So according to one's vasana the soul takes next birth in such an atmosphere which is conducive for its growth.
So it is only logical that only God decides our birth atmosphere, since we mortals have little knowledge about our vasanas. That said, with faith in God, the given varna should be accepted.
As a shudra, i am free to travel abroad for material prosperity. It is not allowed for other varnam people. Though Ovvayar says "Thiraikadal oodiyum thiraviyam thedu" , Manudhrmam recommends staying with in dharma bhoomi for these three varnams.
In spiritual terms, to a shudra and also to a woman, bhakthimargam is open freely. We see immense love of Kannappar and Nandanar towards God.
In Nandanar puranam, Nandanar reaches Chidambaram. But he is unable to enter the city as through out the city priests are conducting homams and yagyams. As an outcast, Nandanar does not have courage to enter the city. He circumabulates the city and sleeps out of exhaustion.
Lord Shiva instructs the priests in their dreams to lit fire and expect Nandanars arrival. At the same time, He instructs Nandanar to enter the pyre to purify his body and to come out as a brahmin, so that he can enter the temple.
This point troubled me heavily. Why should God dislike shudra body? Why brahmin body is required to enter temple? If brahmins say that, we can understand that as a lowly act of a group of people. But why did God insist on such an act?
Gnana margam is open to all other varnams. They can learn vedam and acquire knowledge through vedantic analysis. But as an outcast, Nandanar reached God through pure love. The only thing which separated him and God was Gnana.
Here the brahmins symbolise gnanam. By making him go through the pyre, God bestowed Him with Gnana. As a person with Gnanam and bhakthi, Nandanar took a new birth as brahmin. Here brahminhood only symbolises Gnanam, just as coconut and flowers symbolises prosperity. Coconuts and flowers are in no way superior to the person doing worship, but they are required for worship. Similarly, the Chidambaram brahmins were in no way superior to Nandanar. Brahminhood simply symbolised attainment of Gnana by Nandanar.
I front of very eyes of all brahmins, Nandanar became one with God.