Well that is a good question. Here is how this works: God created angels and human beings with choice. God created perfect angels but he wanted them to love Him not because they were forced to love Him but because they wanted to love and obey Him, which is the same thing that your mom and dad want with you. They want you to love them not because they are forcing you to love them, but because you want to love them.
When you give your dad and mom a kiss before you go to bed, it is not because they say, “If you do not give me a kiss, I am going to beat you up.” They want you to give them that kiss because you love them. Then that kiss really means something to them.
That is the same way with angels. God created angels in such a way that they could love him and serve him or they could choose to disobey and rebel against Him. So they had freedom of choice, and without that kind of freedom of choice love does not mean a whole lot.
Now the angels did not all do the same thing. Some of the angels rebelled against God. They did not want to love and obey Him. They wanted to do what they wanted to do. They wanted to disobey Him, because they thought they knew better. And sometimes even kids think that they know better than their parents, but later on when they grow up, they think: my mom and dad knew what they were talking about. That is the same thing. Satan and the angels rebelled against God, but you know what, they knew what they were doing, because they had a lot of knowledge, and they were in the presence of God, but still they chose to disobey God. And that’s how sin comes into heaven and earth.
Adam and Eve did the same thing. God gave them the ability to choose, and they chose to do the wrong thing, and as a result we now have sin in the world. But the beautiful story of the Bible is that God has given us a way out of sin, and that way out of sin is Jesus Christ. When Jesus Christ comes into our heart, then we have the perfect righteousness of Jesus Christ that covers us so that we can have a relationship with God again.
Then another sign appeared in heaven: an enormous red dragon with seven heads and ten horns and seven crowns on his heads. His tail swept a third of the stars out of the sky and flung them to the earth …And there was war in heaven. Michael and his angels fought against the dragon, and the dragon and his angels fought back. But he was not strong enough, and they lost their place in heaven. The great dragon was hurled down—that ancient serpent called the devil, or Satan, who leads the whole world astray. He was hurled to the earth, and his angels with him (Rev. 12:3, 7-9, NIV).
This blog adapted from “If there is no sin in heaven how did Lucifer fall?”