To be perfectly frank, for me asking, "Why Christ?" is like asking, "Why filet mignon?" when the only other things on the menu are garbage soup a la maggots, day-old road kill, and cow pies.
You see, I grew up as an atheist. I know what life without God is like. I know the emptiness and meaninglessness of a life with no center but self. And I know what it is like to have Christ burst like a fountain into life’s barrenness and not only make sense out of life but also answer every human longing.
And yet, I realize that some ask this question in sincerity, and so I will give it a sincere reply.
Why Christ? Because He is the Way, the Truth and the Life. Because no one comes to the Father except through Him. Because no one else has the words of eternal life.
Why Christ? Because He is God. Because He is the Creator of all things and He holds all things together. Because He is Immanuel, God with us, who left His position of glory with the Father in heaven and came to earth as a man in order to take upon Himself the just penalty we deserved for our sin.
Why Christ? Because He sets the prisoner free and makes the blind to see. Because He is the bread of life, and the one who eats of Him will never hunger again. Because He is the river flowing with living water. Because we live in a broken world and He is the One who has come to restore it.
Why Christ? Because He is the only rock upon which our lives can be built that can be trusted to preserve us through all the troubles of this life. Because He carries His little ones in His arms and shields them from the enemy of their souls.
Why Christ? Because He is the judge of all mankind, who will return some day: "The Lord Jesus will be revealed from heaven with His mighty angels in flaming fire, dealing out retribution to those who do not know God and to those who do not obey the gospel of our Lord Jesus." (2 Thes. 1:7-8)
But if someone takes the question "Why Christ?" to mean "Why do you think Christ is true?", let me say this. Christ clearly and repeatedly claimed to be God, come down from heaven to dwell as a man upon the earth to save sinners. What can be said to these claims? CS Lewis said it well:
"A man who was merely a man and said the sort of things Jesus said would not be a great moral teacher. He would either be a lunatic - on a level with the man who says 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." (Mere Christianity, Book II, Chapter 3)
Liar, lunatic, or Lord. There is no other possibility. Why Christ? Because He is the Lord of the universe. Why Christ? Because He is our only hope.