What are the key differences between the Old Testament and New Testament?

The old testament is before the coming of the Messiah, and its themes centralize around the fact that they still have to sacrifice for their sins because there is no Messiah. The Old Testament makes prophesies about the Messiah's coming. The New Testament focuses on the messiah, Jesus, and how he saves us from our sin. The New Testament fulfills the prophesies promised in the Old Testament. The Old Testament follows the Mosaic Law.
Matthew 5:17 Think not that I am come to destroy the law, or the prophets: I am not come to destroy, but to fulfil. 5:18 For verily I say unto you, Till heaven and earth pass, one jot or one tittle shall in no wise pass from the law, till all be fulfilled. The New Testament Abbrogated the Mosaic Law; Galatians 3:24 Wherefore the law was our schoolmaster to bring us unto Christ, that we might be justified by faith. 3:25 But after that faith is come, we are no longer under a schoolmaster.