If Jesus was Jewish, why aren't Christians Jewish?

Of the major world religions, Christianity and Judaism are likely the most similar. Christianity and Judaism both believe in one God who is almighty, omniscient, omnipresent, eternal, and infinite. Both religions believe in a God who is holy, righteous, and just, while at the same time loving, forgiving, and merciful. Christianity and Judaism share the Hebrew Scriptures (the Old Testament) as the authoritative Word of God, although Christianity includes the New Testament as well. Both Christianity and Judaism believe in the existence of heaven, the eternal dwelling place of the righteous, and hell, the eternal dwelling place of the wicked (although not all Christians and not all Jews believe in the eternality of hell). Christianity and Judaism have basically the same ethical code, commonly known today as Judeo-Christian. Both Judaism and Christianity teach that God has a special plan for the nation of Israel and the Jewish people.

The all-important difference between Christianity and Judaism is the Person of Jesus Christ. Christianity teaches that Jesus Christ is the fulfillment of the Old Testament prophecies of a coming Messiah / Savior (Isaiah 7:14; 9:6-7; Micah 5:2). Judaism often recognizes Jesus as a good teacher, and perhaps even a prophet of God. Judaism does not believe that Jesus was the Messiah. Taking it a step further, Christianity teaches that Jesus was God in the flesh (John 1:1,14; Hebrews 1:8). Christianity teaches that God became a human being in the Person of Jesus Christ so He could lay down His life to pay the price for our sins (Romans 5:8; 2 Corinthians 5:21). Judaism strongly denies that Jesus was God or that such a sacrifice was necessary.

Christianity has a close relationship with Judaism, both historically and theologically. Jesus, the twelve disciples, the author of most of the New Testament, and the members of the earliest Christian churches were all Jews. Jesus' family followed Jewish customs and Jesus frequently quoted the Hebrew Bible. Jesus' followers believed him to be the Messiah, a Jewish figure predicted in the Jewish Bible. (See Christian Beliefs main page and Judaism beliefs main page)

Despite its Jewish origins, it was not long before Christianity regarded itself as something other than a new Jewish sect. The first Christian council, convened by the apostles, concluded that pagan converts to Christianity did not have to follow Jewish ritual laws. Soon, converts to Christianity were almost exclusively pagans and Christianity moved further away from Judaism. Today, theological disagreements between Christians and Jews remain, but efforts are being made towards greater understanding and respect between the two great faiths. The following chart compares the origins, beliefs and practices of Christianity and Judaism.

Reprinted from: http://www.religionfacts.com/christianity/charts/christianity_judaism.htm & http://www.gotquestions.org/difference-Christianity-Judaism.html