[2] D'Costa was appointed a visiting professor of Inter-religious Dialogue at the Pontifical University of Saint Thomas Aquinas, Rome.
[13] He examined the work of key representatives of each of these positions: John Hick as a pluralist, Karl Rahner as an inclusivist, and Hendrik Kraemer as an exclusivist.
[13] D’Costa defended Rahner's inclusivism that held to the universal love of God for all people as well as the necessity of Christ's grace for salvation.
[15] Hence, these positions advocate that all religions are equal, but actually have an explicitly religious exclusivism (in the case of the Dalai Lama, there is no liberation until one has become a De Lug Buddhist monk), but one has endless lifetimes to achieve this; likewise for Radhakrishnan, but in this case (a non-dual Advaitin experience of moksha is required for final release from the cycle of birth and death), or a secular modern exclusivism (an ethical rule, that derives from Kant and stands in judgment upon all religions).
[15] D’Costa defends a trinitarian approach to other religions that refuses to see them as equal or provisional/imperfect forms of revelation or salvific means; nevertheless, he acknowledges the grace of God operative within these traditions in a fragmentary and inchoate manner.
[18] D'Costa argues that invincible ignorance was crucial in moving to a positive attitude to other religions since they were no longer seen to explicitly and knowingly reject Catholic truth.
[18] In relation to Islam, there is a distance from the views of Louis Massignon, while at the same time an affirmation of a creator God who is the final judge.
[19] He establishes the Catholic Church's formal move away from supersessionism to a position that holds the covenant made by God with his people, Israel, is now viewed as valid and effective.
[19] He argues for a tentative minimalist Catholic Zionism while upholding the rights of the Palestinian people and their claim to a nation and state.
[19] He claims that in a post-supersessionist world view, any form of mission or witness that called into question Jewish religious legitimacy would be illegitimate.
[19] D'Costa has followed up on this work by bringing together Faydra Shapiro, an Orthodox Jew, and an international collection of Roman Catholics to reflect on the people, land and state of Israel.
[21] He provides a close reading of Islam as presented through Salman Rushdie’s Satanic Verses and examines artistic representations of the trinity in Hindu and Christian culture.
[8] For example, John Hick has argued that D’Costa's claim that pluralism is just a disguised exclusivism is word play, and fails to deal with the substantial difference involved in the pluralist position.