We exist as a body of believers who hold to the New Testament doctrine of Christianity. Doctrine means teaching, so our teaching and instruction comes from the Bible and the Bible alone. Paul said in 2 Timothy 3:16 that all scripture is from the mouth of God. Therefore, we hold to the things that God said for our understanding of truth.
The mission of the churches of Christ is to teach God's
inspired word without variation to God's created souls in each
generation. There are many paradigms of belief within the umbrella of
faith called Christianity. Some say do what feels right. Others say a
person should be good and that is all that is needed. Still others have
many rituals and rules developed over the years that they say must be
Denominations, or divisions, came from man's decisions to decide how Christianity should be practiced in their time. One says take the Old Testament and the New Testament together and do some of what is taught in both. Others say the Bible taught the people of that period but things are different now. We believe in "rightly dividing the word of truth". This is taught in 2 Timothy 2:15. A study of scripture will show that God gave the Old Testament to a group of people who were the descendants of Abraham. This teaching pointed to Messiah, who was to save the world from their sins. This Messiah is Jesus, who, when He died, brought in the New Testament.
A testament is now called a "Will", or sometimes "Will and Testament". A will goes into affect at the death of the Testator Hebrews 9:16-17. When Jesus died, His Will or Testament came into affect, putting all those who lived after the church began in Acts 2 under the New Testament Luke 16:16.
Therefore we, as New Testament Christians, teach from the words of Jesus and the Apostles the inspired Word from God to people today. Unity is found when people agree that God is right, and His teaching for Christians today is the New Testament.