Different but still Neighbours

I've always struggled with the idea that there is only one way to serve God, and that is the Christian way. As a Jew, Christ surely followed the Ten Commandments, but he also gave us a new, golden one to live by which tells us to love our neighbour as our self. Well, my neighbours, like his at the time, represent many races and religions. They are different from me, but they are my brothers and my sisters. We are one, because God created us all.
C.S. Lewis writes in Mere Christianity, "Is it not frightfully unfair that this new life should be confined to people who have heard of Christ and been able to believe in Him? But the truth is God has not told us what His arrangements about the other people are. We do know that no man can be saved except through Christ; we do not know that only those who know Him can be saved through Him."