Many people today are content to call Jesus “teacher”, but are unwilling to call Him “Lord.” Call Him one prophet among many, and most will not object. Call him a good spiritual or moral teacher, and many will be happy to pay him lip service. But He is Lord; He is God.
In his classic book, Mere Christianity, C.S. Lewis writes,
I am trying here to prevent anyone saying the really foolish thing that people often say about Him: “I’m ready to accept Jesus as a great moral teacher, but I don’t accept His claim to be God.” That is the one thing we must not say. A man who was merely a man and said the sort of things that Jesus said would not be a great moral teacher. He would either be a lunatic – on a level with the man who says that he is a poached egg – or else he would be the Devil of Hell. You must make your choice. Either this man was, and is, the Son of God: or else a madman or something worse. You can shut Him up for a fool, you can spit at Him and kill Him as a demon; or you can fall at His feet and call Him Lord and God. But let us not come with any patronising [sic] nonsense about His being a great human teacher. He has not left that open to us. He did not intend to. (p.45)
In the end, to receive Jesus as nothing more than a good moral teacher is to reject Him as your Savior and Lord; it is to receive a Jesus of your own devising and imagination. He did not come just to teach you or improve you, but to save you from your sins!
The Westminster Shorter Catechism states,
Q. 86. What is faith in Jesus Christ? A. Faith in Jesus Christ is a saving grace, whereby we receive and rest upon him alone for salvation, as he is offered to us in the gospel.
To have faith in Jesus Christ is to receive and rest upon Him alone for salvation. It is to receive Him as He is offered to us in the gospel, as He is offered to us in the holy Scriptures. And the Scriptures are very clear about who He is and about what He came to do – He is God in the flesh come to live and die in the place of sinners, for our salvation!