He asserted, in his "Sri Bhasya", that "purvapaksin" (previous schools) selectively interpret those Upanishadic passages that support their monistic interpretation, and ignore those passages that support the pluralism interpretation. There is no reason, stated Ramanuja, to prefer one part of a scripture and not other, the whole of the scripture must be considered on par. One cannot, according to Ramanuja, attempt to give interpretations of isolated portions of any scripture. Rather, the scripture must be considered one integrated corpus, expressing a consistent doctrine. The Vedic literature, asserted Ramanuja, mention both plurality and oneness, therefore the truth must incorporate pluralism and monism, or qualified monism. This method of scripture interpretation distinguishes Ramanuja from Adi Shankara. Shankara's exegetical approach "Samanvayat Tatparya Linga" with "Anvaya-Vyatireka", states that for proper understanding all texts must be examined in their entirety and then their intent established by six characteristics, which includes studying what is stated by the author to be his goal, what he repeats in his explanation, then what he states as conclusion and whether it can be epistemically verified. Not everything in any text, states Shankara, has equal weight and some ideas are the essence of any expert's textual testimony. This philosophical difference in scriptural studies, helped Shankara conclude that the Principal Upanishads primarily teach monism with teachings such as "Tat tvam asi", while helping Ramanuja conclude that qualified monism is at the foundation of Hindu spirituality. John Carman, a professor at the Harvard Divinity School, states that some of the similarities in salvation ideas in Sri Vaishnavism and Protestant Christian doctrines of divine grace are striking. Both accept God as a personal concept, accept devotee's ability to relate to this God without human intermediaries, and accept the idea of "sola gratia" – salvation through faith by the grace of God alone, such as those found in Martin Luther's teachings. While both Sri Vaishnavism and Protestant Christianity accept a supreme God and shares ideas on the nature of salvation, they differ in their specifics about incarnation such as Jesus Christ being the only incarnation in Christianity, while Sri Vaishnavism accepts many incarnations (avatar) of Vishnu. Christian missionaries in 19th century colonial British India, noted the many similarities and attempted to express the theology of Christianity as a "bhakti marga" to Hindus, along the lines of Sri Vaishnavism, in their mission to convert them from Hinduism to Christianity.