God is eternal, God does not change. From the book of Malachi to the gospels, there was no change in God, except that God sent His Son to complete a plan God had for us. That plan includes the need for us to be forgiven of our sins that keep us from living a triumphant full life here and after we leave this life.
God had made partial atonement for sin available through symbolizing the blood of Christ by the blood of animals. God often uses the physical to reflect and teach the spiritual. People followed the physical at the temple, but they couldn't really understand the spiritual side of what they were doing. Through the gospel (Christ) we can understand more fully. Our understanding is still lacking. God gave us the epistles to try to clear it up for us, but for lots of people they only mix them up more.
The Torah, the Ten Commandments, and what the feasts teach has not been done away with at all. They tell us about God, things we have to know. All the laws given in the Torah are based on the absolute love God has for His Creation, on their having a safe, plentiful world to live in while we are here. People often used doing these things as enough, and through Christ we learn that you can go through the physical motions without any of the love that must be in all. As the epistles try to teach this, people say the motions are done away with. We are to know that God looks at our hearts, not the motions. Some people still use the motions to learn of God by, or to remind them of what God wants of them.