Soul has no caste : The canonical definition of Braahman is "One Who Knows The Brahm".

Soul has no caste : the ultimate purpose of Ved is Spiritual Knowledge, and nowhere it is written that only Braahman have a right to attain enlightenment. But those who have attained enlightenment are real Braahman, whatever be their caste, although such enlightened persons do not enter into the caste ridden society and strive for Moksh.

Soul has no caste : Chhaandogya Upanishad has a story of Raikwa Shoodra. A Kshatriya King was called Shoodra by a cart-driver Raikwa who was a Brahm Gyaanee, and this King made Raikwa his spiritual guru. By birth, Raikwa was a Shoodra but taught Upanishadik knowledge to a Dwij. This story is part of Vaidik literature, like that of Satyakaam Jaabaali.

Soul has no caste, but birth is an undeniable biological fact. Karmkaand were performed by caste-Braahman only, controlled by real Brahm Gyaanee who possessed the power to get desired results for the Yajamaan. Producing Apoorv fruits from Yagya was a great feat and Yajamaan did not want to take risk. Hence, only Braahman were allowed to perform Yagya. But in Kali Yug, Braahman lost Brahm Gyaan, except for rare individuals who are not even consulted in Yagya, and Karm Kaand became a profession, devoid of its power.

Soul has no caste-based Sanskaar : Sanskaar is characteristics of the Sookshm body, not of soul. Tapasyaa is a powerful agent and can transform Sanskaar. Rig Ved (X-191) says : Sat and Rit are born out of Tap. Vishwaamitra and Vaalmeeki became Braahman due to their Tapasyaa only. Those non-Dwij who want Vaidik knowledge must follow the austere ancient rules and should not mimic the degenerated Braahmn of Kali Yug who are worse than Shoodra of yore.