Jesus drove the money changers out of the Temple, because they were violating the Temple with their presence and their actions -- preying on poor people there.
Jesus' primary message was love (Love thy neighbor as thyself), peace, and the path to righteousness (Sell all your goods, give them to the poor, and follow me -- no man comes to the Father but through me).
The OT is far more violent, but given for a specific people at a specific time and those things are not ordered for modern day Christianity -- modern day Christians are commanded to spread the gospel to the ends of the earth, but also to be meek, and every example we have after Peter's ill-advised attempt to defend Christ the night of his crucifixion is an example of following the law where possible and being peaceful.