It started after the death of Jesus Christ.
The Old Testament is the basis of Christianity.
Christianity
Word Christianity was mentioned in the Old Testament the exact number of times that it was mentioned in the New Testament - zero.
Christianity shares the Old Testament with Judaism, and the New Testament is specific to Christianity.
The scriptures of Christianity are contained in the Bible: 39 books of the Old Testament and 27 books of the New Testament.
All look to the Old Testament as the root of their beliefs
The New Testament begins after the Old Testament, specifically after the events described in the book of Malachi.
The Old Testament was completed before the advent of Christianity, and the position of pastor is a Christian office. The Old Testament does not mention Christian pastors.
The holy book of Christianity is the Bible. It has two main divisions - the Old Testament and the New Testament. The Old Testament is basically the same as the Tanakh the religious book of Judaism
Judaism uses the Old Testament, or Hebrew Bible. Christianity uses a Bible containing both the Old Testament and the New Testament.
Baptism, as it is understood in Christianity, was not practiced in the Old Testament. The concept of baptism was introduced in the New Testament as a ritual symbolizing purification and initiation into the Christian faith.
Judaism-believes the Old Testament and that the messiah which the Old Testament fortells has not come. Christianity- believes the Old Testament and the New Testament and that the Messiah which the Old Testament fortells has already come. John 3:16 (in New Testament) "For God so loved the world that he gave his only begotten Son, that who so ever believes in Him shall not parish but have everlasting life. " Jesus Christ is this Son/Messiah, according to the New Testament.