From John Piper’s The Passion of Jesus Christ: Fifty Reasons Why He Came to Die, Chapter 50, page 118 (you can download the whole book from his website – how generous!)
But the most astonishing thing is that evil and suffering were Christ’s appointed way of victory over evil and suffering. Every act of treachery and brutality against Jesus was sinful and evil.
But God was in it. The Bible says, “Jesus [was] delivered up [to death] according to the definite plan and foreknowledge of God” (Acts 2:23). The lash on his back, the thorns on his head, the spit on his cheek, the bruises on his face, the nails in his hands, the spear in his side, the scorn of rulers, the betrayal of his friend, the desertion by his disciples—these were all the result of sin, and all designed by God to destroy the power of sin. “Herod and Pontius Pilate, along with the Gentiles and the peoples of Israel, [did] whatever your hand and your plan had predestined to take place” (Acts 4:27-28). There is no greater sin than to hate and kill the Son of God. There was no greater suffering nor any greater innocence than the suffering and innocence of Christ. Yet God was in it all. “It was the will of the LORD to crush him” (Isaiah 53:10). His aim, through evil and suffering, was to destroy evil and suffering. “With his stripes we are healed” (Isaiah 53:5).
I thought to myself, “But John, in the Bible Jesus says that a kingdom divided against itself cannot stand. That Satan cannot cast out Satan, or else he will fall, and that to rob a strong man of his possessions, one must first tie him up (Matthew 12:22-29). How does that all work?” Well, I then thought, of course it works. If God uses evil and suffering to destroy evil and suffering, it is as Christ said, evil and suffering will cease. In order to make evil and suffering cease, it is necessary to divide Satan’s kingdom against itself. Satan would not fight against himself unless God were puppeteering him, or else he would orchestrate the doom of his own kingdom! Therefore God must use Satan to cast out Satan. God is the strong man who has tied Satan up.
How then do we apply this when people ask “Why does a loving God allow suffering in the world?”. Here is a theory based on my understanding of Scripture.
Firstly, God is the source of all good. God made the world in the beginning and saw that it was good. Suffering is a result of of sin (or “evil”), which is rebellion against God and his good way of running the world. Rebellion was born when one of the Intelligences in the heavens caused an uprising against God and preyed upon humanity and wooed it away from God, making it rebellious in turn. We call this Intelligence a lot of things; Satan is perhaps the most convenient; Beelzebub, or ‘the devil’, are others. To remove all rebellion from the world, God would have to remove all people who had ever rebelled against him, and God didn’t want to destroy them because he loved them. So God sent Jesus to die to expiate the rebellion of those who would come back to him, to satisfy his requirements for justice so that he could take them back. Now when God sent Jesus, that is, his spirit in human flesh, people accused him of being a partisan of Satan when they saw him liberating people from demons (Satan’s spiritual partisans). Essentially, Jesus was answering to the assertion that God is evil. Jesus said that if he was casting Satan’s partisans out of people he could not be working on behalf of Satan’s Kingdom, because a Kingdom divided against itself will fall. Furthermore, he said, to tie up a strong man and steal his possessions one must first tie up the strong man. God uses this tactic to destroy rebellion, and with it, suffering. He tied up Satan, then used sin, and with it, suffering, against itself to destroy it.
God tied up Satan by laying all sin (or evil, or rebelliousness, which causes suffering) on Jesus, that perfect representation of himself. In letting Satan destroy Jesus, God let sin destroy sin, so that those people who resolved not to sin anymore could claim the destruction of sin through Jesus as their own, and not be destroyed themselves. God sent his man to face the penalty for human rebellion by his own justice system, and this would satisfy its requirements so that he could save the people he loved from it and live with them forever. He raised Jesus back to life again and promised his faithful that they would be raised to life to enjoy this eternal life with him.
What God had left to do was to rid the world of the rest of its rebellion and suffering, and through Jesus he could do this by encouraging rebellious people to repent and reconciling them to him thereafter. My theory is that God now puppeteers sin and with it, suffering, although he hates these things. They are necessary for now because people, seeing that they are suffering, might regard the joy of God’s true partisans and want it for themselves. They might see that it came from God and decide to sin no more, accepting Jesus’ penalty as their own. So in this way, God is using suffering to bring people to himself, so that rebellion which causes suffering can be eradicated without him having to destroy all of mankind.
I stress that this is all based on my current understanding of Scripture. It is an answer that I can give, and though it seems to make sense to me, I acknowledge that God’s ways are nothing like our ways, and that his thoughts are not like our thoughts.