In response to Spider AL, the reason the Old Testament is lumped in with the teachings of Jesus is that the prophecies that told of his coming were in there. They were like the prelogue, the backstory so to speak. You saw that Jesus fulfilled all those prophecies and you saw the kind of world he was coming into.
When Jesus was cruxified, and rose on the third day (note: this is often the time where I start to get flamed when I make this post. This is assuming Cathlolic dogma to be true), he made a new covenant. All the stuff of the old testament didn't fly out the window exactly, but it was replaced by the New Covenant of Jesus.
A choice quote from that website...
"Comment: Christians have a relationship with God, and that relationship is on the basis of the new covenant, not the old.
In the new covenant, God gives some commands and makes some promises, and those promises have already begun to be fulfilled. The Holy Spirit is given to us not only to transform our hearts but also as a down payment of greater blessings to come (2 Cor. 1:22). Just as the old covenant was made before all the promises were delivered, so also the new covenant has been established before all its promises are completely given.
The new covenant was ratified through the blood of Jesus Christ. Not only did his death pay for our sins, it also ended the old covenant and began the new.
When we drink the wine in commemoration of Jesus' death, we show our acceptance of the new covenant, including the forgiveness that is given because of his shed blood."
So, Fundamentalist Christians
are technically going against their own religion when they preach the Old Testament and deny the pacifistic teachings of Jesus in the New Testament. Fundamentalist Christians (the hardcore ones) make up probably less than 1% of the entire Christian Religion. A lot less than one percent I'm guessing (just a guess, I don't know any statistics on this). They are much like the followers of Radical Islam...spinoffs from the main stream school of thought who hold radically different and often hateful beliefs. Don't think for a minute that the Hardcore Atheists are much different. They see their belief as 100% in the right and are hostile to others in the same manner that Fundies are hostile to people who don't share their beliefs.
One last choice quote from the website above...
"When Jesus established the new covenant, did he set aside the first covenant? Heb. 8:13. Is the old covenant declared obsolete? Same verse.
Comment: Here we see the reason that Christians are not required to keep some of God's laws -- because God has declared some of them obsolete.
Since God has grouped his laws into covenants, it is essential that we understand the covenants if we want to understand why some Old Testament laws no longer need to be kept. Much of the Old Testament is built on the old covenant, and much of the New Testament is about the new covenant. Although a covenant is not exactly the same as a testament, the concepts are so closely related that a single Greek word is used for both."