If we see everything in the light of the centrality of Christ, we can see God's plan, who created everything "for him and in expectation of him." And we can see the actions of Satan, the enemy, the tempter, the accuser. By means of his temptation, evil, pain, sin, and death entered the world. It is in this context that we are able to see the restoration of God's plan, which Christ accomplished at the cost of his blood.
In this context, we are made aware of the power of the devil. Jesus calls him "the prince of this world" (Jn 12:31, 14:30, 16:11). John affirms that "the whole world is in the power of the evil one" (1 Jn 5:19); by "the world" John means everything that is opposed to God. Satan was the brightest of the angels; he became the most evil of the devils and their chief. The demons remain bound to the same strict hierarchy that was given them when they were angels: principalities, thrones, dominions, and so on (Col 1:16). However, while the angels, whose chief is Michael, are bound by a hierarchy of love, the demons live under a rule of slavery.
We are also made aware of the action of Christ, who shattered the reign of Satan and established the kingdom of God. This is why the instances where Jesus freed those possessed by demons become particularly important. When Peter teaches Cornelius about Christ, he does not mention any miracle besides the fact that he cured "all those who had fallen under the power of the devil" (Acts 10:38). We understand, then, why the first authority that Jesus gave his apostles was the power to expel demons (Mt 10:1). We can make the same statement for all believers: "These are the signs that will be associated with believers: in my name they will cast out devils" (Mk 16:17). Thus Jesus heals and reestablishes the divine plan that had been ruined by the rebellion of some of the angels and by our forefathers.
We must make this abundantly clear: evil, suffering, death, and hell (that is, eternal damnation in everlasting torment) are not acts of God. I want to expand on this point. One day Father Candido was expelling a demon. Toward the end of the exorcism, he turned to the evil spirit and sarcastically told him, "Get out of here. The Lord has already prepared a nice, well-heated house for you!" At this, the demon answered, "You do not know anything! It wasn't he (God) who made hell. It was us. He had not even thought about it." Similarly, on another occasion, while I was questioning a demon to know whether he had contributed to the creation of hell, I received this answer: "All of us cooperated."
Christ's centrality in the plan of creation, and its restoration through redemption, is fundamental to understanding God's plan and the end of the world. Angels and men received an intelligent and free nature. When I am told (by those who confuse predestination with God's providence) that God already knows who will be saved and who will be damned, and therefore anything we do is useless, I usually answer with four truths that the Bible spells out for us: God wants that everyone be saved; no one is predestined to go to hell; Jesus died for everyone; and everyone is given sufficient graces for salvation.
Read it all.