The Problem of Evil
I have never thought about how the doctrines of original sin and free will are related and what the implications of these doctrines are.
As Catholics, we believe that pain, suffering and death entered the world (Genesis 3) because of the sin of Adam and Eve. We inherited a weakened body that is vulnerable, where before the fall of Adam, God created us "very good" as Genesis 1 tells us. St. Ambrose said that God allows us to die to limit the amount of suffering we have to endure in this world. Death, then, is a loving method of reuniting ourselves to God eternally. Therefore, pain, suffering and death are part of the human condition.
The Old Testament paints God as wrathful; and always smiting people for their disobedience. How can God be both loving, merciful, kind and yet be punishing? That is a contradiction. Without the doctrines of original sin and free will, we would have to believe that suffering is inflicted by a vindictive God as punishment for sin. In Catholic theology, punishment for sin is the loss of grace that helps us to grow in virtue, and if serious and unrepented, will result in the loss of salvation. In this way, mortal sin is a far greater punishment than temporary physical sickness. On the other hand, God is patient and usually gives us a lot of time to repent. Hopefully, the loss of God's friendship leads to conversion.
Because I love my children, I discipline them with natural consequences, such as grounding them from being with friends and watching TV. My children see me as a cruel and vindictive. That would be true if I abused them physically, but I am merely taking away a privilege. They don't understand that I am trying to teach them to do the right thing out of love for them. They don't see the big picture. I hope they will see it when they become parents.
It is their free will that has resulted in the consequences. By choosing to disobey, they are choosing the punishment. It is the same way when we sin. We choose to disobey God, so we deserve to lose God's grace. Sinners may think God is mean and vengeful, but that is a failure to take responsibility for their choices.
Sin does often have physical side effects. Sexual sins may result in sexually transmitted diseases. A drinking binge causes brain cells to die and, if it becomes a habit, can lead to cirrhosis of the liver. These sins may also have an emotional consequence of a wrecked relationship. However, these illnesses and pain are not inflicted by God for punishing the sin. They are a result of free will.
In Catholic theology, Original sin deprived us of grace and weakened us, but did not make us totally depraved. We have the freedom to do evil or the freedom to chose good. The benefit of obedience to God is that we grow in holiness and friendship with Him. We enjoy the guidance of the Holy Spirit which dwells within us. We are members of God's family and so we receive an inheritance of eternal life which is a free gift. Sirach 15:11-20 supports the doctrine of free will. "Say not: "It was God's doing that I fell away"; for what he hates he does not do. Say not: "It was he who set me astray"; for he has no need of wicked man. Abominable wickedness the Lord hates, he does not let it befall those who fear him. When God, in the beginning, created man, he made him subject to his own free choice. If you choose you can keep the commandments; it is loyalty to do his will. There are set before you fire and water; to whichever you choose, stretch forth your hand. Before man are life and death, whichever he chooses shall be given him. Immense is the wisdom of the LORD; he is mighty in power, and all-seeing. The eyes of God see all he has made; he understands man's every deed. No man does he command to sin, to none does he give strength for lies."
If instead we believed that we are incapable of doing anything but sin, it would be indeed a cruel God for punishing us when we can't do anything good. That would be like a father that beats his developmentally disabled son for disobeying him in not doing his trigonometry homework. That is not my idea of a good, loving father. I could not praise a God that treated us that way.
Does God punish us for sin by inflicting sickness? In Job 1:12, God told Satan "do not lay a hand upon his person." Satan disobeys God. Job 2:7 says, "So Satan went forth from the presence of the LORD and smote Job with severe boils from the soles of his feet to the crown of his head."
The last chapter of the book of Job also gives us a clue about suffering. Job 42:7-8 says, "And it came to pass after the Lord had spoken these words to Job, that the Lord said to Eliphaz the Temanite, "I am angry with you and with your two friends; for you have not spoken rightly concerning me, as has my servant Job. Now, therefore, take seven bullocks and seven rams, and go to my servant Job, and offer up a holocaust for yourselves; and let my servant Job pray for you; for his prayer I will accept, not to punish you severely. For you have not spoken rightly concerning me, as has my servant Job." If you remember, Eliphaz and two other of Job's friends had told Job that he must have sinned or God would not have caused the loss of his family and property. So the Lord tells Job's friends that they were not telling the truth; that is, suffering in this world is not necessarily a punishment for sin. The just man will also suffer. The Lord does not owe us an explanation. In humility, we trust that sometimes God allows us to suffer when something really good can come from it. In the end of Job, God restores everything to Job. Job has set a good example to others of faithfulness and has learned humility. Job 42:10 "the Lord restored the prosperity of Job, after he had prayed for his friends; the Lord even gave to Job twice as much as he had before." God knew a good result would come from this test. Even if Job had not been blessed by return of his fortune, in Job 19:25-26 it says Job had faith that all would be made just in the next life. "For I know that my Redeemer lives, and at last he will stand upon the earth; and after my skin has been thus destroyed, then from my flesh I shall see God," He would not suffer forever.
Another aspect of suffering is that it can become a way of teaching us what we can't learn otherwise. Instead of asking, "Why me?" and wallowing in self-pity, perhaps we need to ask "Why not me?" Though we can't totally avoid suffering, when it comes to us, we can try to get something good out of it. Perhaps we can learn to be more grateful for what is still good in our lives. Perhaps we can be more empathic to those who are suffering in the same way as we are. Perhaps we can grow in the virtue of patience. Perhaps, like the Prodigal Son, it leads to repentance. If there can be good effects from suffering, we should ask "Who among us is so good that we can't gain something from a little pain?" Some saints practiced fasting for this reason. God is so good to us, but we tend to forget that he treats us better than we deserve. We frequently react with self-pity.
Self-pity in the face of suffering increases our pain. In the Beatitudes, Jesus tells us that we are not alone in our suffering. "Rejoice and be glad, for your reward will be great in heaven. Thus they persecuted the prophets who were before you." The Catechism, no. 164, says, "Our experiences of evil and suffering, injustice, and death, seem to contradict the Good News; they can shake our faith and become a temptation against it" . God provided a remedy for self-pity. Col 1:24 says, "Now I rejoice in what was suffered for you, and I fill up in my flesh what is still lacking in regard to Christ's afflictions, for the sake of his body, which is the church." While some believe that nothing is lacking in Christ's suffering, this verse says otherwise. We can offer our sufferings in union with the sufferings of Christ for the redemption of others. We can bear our sufferings patiently while offering them to God for the benefit of others. Catholics have a term for this called redemptive suffering. The suffering of Christ gives meaning to our suffering.
Pope John Paul II's encyclical, Salvifici Doloris, "On the Christian Meaning of Human Suffering" agrees with this. This encyclical also says that while we have revelation about why mankind suffers, the reason a particular individual suffers is a mystery. In the same way, each individual will react differently. The challenge of suffering is to react in a faithful, hopeful, and loving way. That requires grace, so let us ask for the Lord's help daily to carry our cross.