If you’re wanting to engage more with the topic of pluralism and the gospel, you can’t go wrong with Leslie Newbigin. Newbigin was an internationally esteemed missionary, theologian and apologist. Here’s a few good starting places:
Foolishness to Greeks: the Gospel in Western Culture
The Gospel in a Pluralist Society
Proper Confidence: Faith, Doubt, and Certainty in Christian Discipleship
Trinity Fellowship 