Christianity is the only religion in the world that claims that man is utterly incapable of doing anything to commend himself to God, and earn any merit in God’s site. Christianity is also the only religion in the world that points to a person—Jesus Christ—as being the only mediator between God and man. Every other religion in the world urges people to live as holy and beneficent a life as they can manage, and trust that being a mostly good person will be sufficient for their salvation.
Clearly both positions cannot be true. Man cannot be simultaneously able and completely unable to do enough good works for a relationship with God. Jesus’ claims of being the only way to God are either true or false. In that sense, Christianity is exclusive.