Why is Christianity a narrow concept?

Christianity is a narrow concept because Scripture declares there is no other name given under heaven among men whereby we must be saved. It does not allow for salvation through Muslim, Shinto, or Hindu paths, so the way is exclusive and absolute, narrowed to one name.

Les explains that this is a narrow book and Christianity is a narrow concept. It does not reach out and say it doesn't matter if you're Muslim, Shinto, or Hindu and you can still profess Christianity. That doesn't work, because the Scripture says there is no other name given under heaven among men whereby we must be saved. That narrows it down, yet it is absolute. Les also stresses the absoluteness of the word of God. He notes that God doesn't force anyone: old Adam reigned under death and misery, but grace reigns like a king through righteousness unto eternal life by Jesus Christ our Lord. The choice is between old Adam and God's grace, and believers should be ready with Scripture as the Lord creates interest.

Acts 4:12

Neither is there salvation in any other: for there is none other name under heaven given among men, whereby we must be saved.

Why is Christianity called exclusivist, and is that accusation fair?

The charge arises because salvation is grounded solely in Jesus Christ. The claim is that there is no other name given among men whereby we must be saved, and that salvation is Jesus Christ plus nothing, received by faith in His finished work. The accusation is fair because that exclusive claim is affirmed.