Prior to Paul appointing himself as an Apostle and breaking ways with the Jewish followers of Jesus in Jerusalem there was only the Old Testament. That and the books not made part of the Bible were the only scripture.
Then Paul and his followers, including the zealot John, deified Jesus and wrote the New Testament. The New Testament is Christian scripture. It is about worshippers of Jesus, for worshippers of Jesus, written by worshippers of Jesus.
Christianity is the worship of Jesus as the Sovereign Lord and Savior of the Universe. Christians spend as much time talking about YHWH as Jehovah's Witnesses spend speaking about Jesus and his Gospel. Vanderhoven7 and SeaBreeze do a wonderful job of proving that modern Christianity is the descendent of the early form of Christianity that survived. There were several types of Christianity with varying beliefs on the divinity of Jesus, but in the end the version that raised Jesus to the position of God, Creator, Savior reigned supreme.
Jehovah's Witnesses are obsessed with the earliest form worship that the followers of Jesus had. They were basically practicing Jews who also accepted Jesus' teachings. They still celebrated the Jewish festivals and went to the temple. That is why they were hated by the Sadducees, and Pharisees. It was their job to keep Judaism pure and free from non-Judaic religious belief or practice. Jehovah's Witnesses are an offshoot of that early, brief period that existed shortly after Jesus death.