Have you read about or heard about something in the Bible that you don't completely understand? There’s a lot of big ideas in the Bible like that. One thing that took me a long time was the idea of God’s “covenant”. Outside of the Bible, a covenant is an important promise between two people that lasts a long time, sometimes forever. They promise to do things for each other. For example, your parents' marriage is a covenant; they promise to love each other and take care of each other.
In the Bible, a covenant is a way to talk about God’s relationship with His people. In the Old Testament, His people were Israel; and in the New Testament and now, it’s everyone who is saved by Jesus and follows His teaching. The covenant in the Bible says what God will do for His people, and what He expects His people to do, like love Him and each other, obey Him, things like that.
The Old Testament covenant was sometimes called the Law of Moses, and it's written down in the first five books of the Old Testament: Genesis, Exodus, Leviticus, Numbers, and Deuteronomy. The most important laws were the Ten Commandments, and then there were many more laws that told the Israelites how to live and how to worship God. If the Israelites were faithful to God by obeying the laws, then He would protect them from being invaded by other countries, He would keep their crops healthy and productive, and He would make sure there was peace in their land. Unfortunately, Israel was not always faithful, and because of that God used other countries to discipline Israel so they would ask for forgiveness and obey Him again.
When Jesus came to earth and died to save everyone from going to hell for the bad things they've done, He started the new covenant. Sometimes people describe it as the "covenant of love" because Jesus loved us so much, He died for us. Everyone, including you and me, has broken God's law, and someone has to be punished for those wrong things. That's why Jesus died: He was punished for the bad stuff you and I have done, even though He didn't do anything wrong. He wants you to join the new covenant of love. If you realize that you've done a lot of bad stuff and you want to follow Jesus, you can read more about that here.