Don’t forget that God is the one who cast Satan out of heaven to the earth. He could have put Satan anywhere in the universe or incarcerated him forever. But He didn’t. Why? Because God wanted to use Satan to accomplish His ultimate goal—the goal one day to have a big family of free moral agents who would love Him, having chosen to serve Him.
If God wanted a family of children who would love Him, then two things were required. First, He had to create people with free wills, because the foundation of love is free will. Robots and machines can’t love.
Second, He had to test them in an environment where they would be faced with a choice to obey or disobey, to love or hate Him. Free moral agents must be tested. And if there is going to be a test of loyalty, there must exist a temptation to disloyalty. Thus, we begin to understand why God placed Satan on the earth. Satan would serve as the alternate choice for humanity’s allegiance. He would be permitted (with certain limitations) to influence anyone who was receptive to his lies. Everyone would be faced with the choice: Will I believe God or Satan? Will I serve God or Satan? Whether people realize it or not, they have all made a decision already. Our job is to encourage people who have made the wrong decision to repent and believe the gospel, making the right decision.
Is this not what happened in the Garden of Eden? God placed the tree of the knowledge of good and evil there and then forbade Adam and Eve to eat from it. If God didn’t want them to eat from it, why did He place it there? The answer is that it served as a test.
We also note that Satan was permitted by God to tempt Eve. Again, if loyalty is to be tested, there must exist the temptation to be disloyal. Satan lied to Eve and she believed him, and so at the same time, she decided not to believe what God had said. The result? The first free moral agents revealed the disloyalty that was in their hearts.
In a similar manner, every free moral agent is tested throughout his or her lifetime. God has revealed Himself through His creation, and so everyone can see that there is an awesome God who exists (see Rom. 1:19-20). God has given every one of us a conscience, and in our hearts, we know right from wrong (see Rom. 2:14-16). Satan and his evil spirits are permitted, in a limited manner, to lie to and tempt people. The result is that every free moral agent is tested.
The sad truth of the matter is that every free moral agent has rebelled and “exchanged the truth of God for a lie” (Rom. 1:25). We can thank God, however, that He has provided a ransom for our sins and a way to be born into His family. Jesus’ sacrificial death is the only and all-sufficient answer to our problem.