This is a very simple explanation of the theology of healing. There are lots of great books out which do a far better job of explaining this subject. A good (free) place to start is with F.F. Bosworth’s Christ the Healer (PDF, audiobook).
To understand healing, we first look at how God originally made the world. The Bible (in Genesis) says God created everything and called it "very good" (Genesis 1:31). In the beginning, people lived in perfect friendship with God and each other. There was no sin, sickness, pain, or death. Everything was whole and healthy because that's how God, the source of life, designed it. Sickness wasn't part of God's original, perfect plan.
Things changed when the first humans, Adam and Eve, disobeyed God (Genesis 3). This event, often called "the Fall," broke the perfect connection between people and God. Sin entered the world, and with it came bad things like separation from God, suffering, sickness, and eventually, physical death. So, from a Christian viewpoint, sickness is one result of this brokenness that came into the world through sin, messing up God's perfect creation.
The center of Christian belief is what Jesus Christ did. Christians believe His death on the cross was a payment for everyone's sins, fixing the relationship between people and God. Importantly, many believe Jesus' sacrifice dealt with both sin and its results, like sickness.
A verse in the Bible often used to explain this is Isaiah 53:4-5, written hundreds of years before Jesus. It says the promised savior would take our sicknesses and pains, and "by his wounds we are healed." The New Testament connects this verse directly to Jesus healing people (Matthew 8:17).
Also, the Greek word often translated as "saved" in the New Testament is sōzō (σῴζω). This word means more than just being saved from sin; it can also mean being rescued, kept safe, healed, or made completely whole. So, when the Bible talks about salvation through Jesus, it often means wholeness for the entire person—spirit, mind, and body. Jesus' death on the cross made forgiveness and physical healing possible. The many miracles of healing Jesus did when He was on Earth showed this connection and gave a glimpse of the total rescue He came to bring.
Jesus didn't just heal people Himself; He told His followers to do it too. He sent His disciples out to "tell people about the kingdom of God and to heal the sick" (Luke 9:2). When Jesus gave His followers the job of telling the world about Him (the Great Commission), healing was part of showing God's power (Matthew 28:18-20).
The book of Acts in the Bible shows the first Christians continuing Jesus' work of healing. These healings were signs that God's Kingdom was real and active, proving their message was true. The later letters in the New Testament also tell Christians to pray for the sick. James 5:14-16 clearly instructs believers to pray for sick people, mentioning that "the prayer offered in faith will make the sick person well (sōzō)."
Healing is seen as something God wants to do now, not just something Christians hope for in the distant future. When God heals someone today, it's considered an act of His love and power breaking into our broken world. It's like a preview or a sign pointing to the ultimate, complete healing that Christians believe will happen when Jesus returns. At that time, believers will receive perfect resurrection bodies, and there will be no more sickness, pain, or death forever (Revelation 21:4). So, praying for healing today is part of experiencing and showing a little bit of that future perfect Kingdom right now.
In Simple Terms:
God originally made a perfect world with no sickness.
Human disobedience (sin) brought sickness and death into the world.
Jesus' death on the cross dealt with both sin and sickness, offering complete wholeness (sōzō).
Jesus told His followers to heal the sick as part of sharing God's Kingdom.
Healing today is a sign of God's love and power, pointing to the perfect healing that will come in the future resurrection.