As we venture into the lessons of the New Testament, we find that some may question, "Didn't God's people already have a law? Wasn't that enough?" In order to answer this question, we look to the book of Hebrews, which is in the New Testament.
Hebrews 1:1, 2 tells us that God did, indeed, talk to His people in different ways at different times, but now--in these last days--God talks to us through His Son, Jesus Christ. God appointed His Son as heir of all things. Jesus was and is better than the angel who spoke to the men under the Old Law (Hebrews 1:3, 4). Under this Old Law, God spoke to His people through prophets, individuals, and other means such as a burning bush or a donkey, but now there is no need to speak in those ways because we have Christ's law or a new testament in the Bible.
Yes, God's people were governed under the Law of Moses until Jesus died on the cross, taking that first law out of the way and establishing the second law, His law, which was a better law (Hebrews 7:22). Jesus is now the mediator--or the go-between--of a better covenant with better promises (Hebrews 8:6). As a better covenant, there is no need to offer animals as sacrifices which were once required under the Law of Moses because Jesus was offered once and for all as a perfect sacrifice to bear the sins of all mankind under both testaments (Hebrews 9:28).
The Old Testament was written for our learning that we might have hope (Romans 15:4) and as a schoolmaster to bring us to Christ (Galatians 3:24). We can learn from those Old Testament characters like Moses, David and Elijah, yet we still need the New Testament to lead us to Christ that we might be saved by obeying His will.